Cardiac IKs as repolarization reserve plays a role in gender difference of diabetic QT prolongation

AIM: To explore the basic ionic mechanisms underlying long-QT syndrome by observing the changes of slowly activating outward rectifying potassium current (I_Ks) and its proteins in abnormal QT prolongation in different genders of diabetic rabbits.METHODS: A single injection of pre-warmed (37 ℃) alloxan (140 mg/kg) was used to establish a rabbit model of insulin-dependent diabetes mellitus. Eight weeks after alloxan injection, the levels of blood glucose in the rabbits were monitored and standard lead II electrocardiogram was recorded. The myocardial cells were isolated from the ventricle of the rabbits via enzymatic digestion. Whole-cell patch clamp technique was performed to study the action potential duration (APD) and I_Ks. The changes of both KvLQT1 and mink proteins were detected by Western blotting analysis.RESULTS: The QT interval and APD were prolonged apparently both in male and female diabetic rabbits. The increased APD/QT-I of the male diabetic rabbits is more remarkable than that of the female. The I_Ks step current density of the male diabetic rabbits was decreased at test potentials ranging from+40 mV to+70 mV compared with that of the control animals (P<0.05), which was lowered from (3.08±0.67) pA/pF (n=17) to (1.27±0.20) pA/pF (n=16) at+70 mV. However, the I_Ks step current density of the female diabetic rabbits was increased at test potentials ranging from 0 mV to+70 mV compared with that of control group (P<0.05), which was increased from (1.56±0.20) pA/pF (n=13) to (3.65±0.50) pA/PF (n=14) at+70 mV. The expression of KvLQT1 and mink in male diabetic group decreased by 21.6% and 18.5%, respectively. However, the expression of KvLQT1 and mink in female diabetic group were increased by 42.3% and 20.5%, respectively.CONCLUSION: The I_Ks may be a protective factor in the early period of diabetic development in female rabbits. As a repolarization reserve, cardiac I_Ks is likely to restrict the effects of excessively slowing repolarization.     

Changes of potassium currents in rabbit ventricle with healed myocardial infarction

AIM: To elucidate the mechanism of arrhythmia in healed myocardial infarction (HMI), and to investigate the changes of action potential duration (APD),transient outward potassium current (I_to), delayed rectifier potassium current (I_K) and inward rectifier potassium current (I_K1) of left ventricular myocytes in noninfarcted zone of HMI. METHODS: 12 rabbits were randomly assigned in two groups: HMI group (thoracotomy and ligation of the circumflex coronary); sham-operated group (thoracotomy but no conorary ligation). 3 months after operation, whole cell patch clamp technique was used to record APD, I_to, I_K and I_K1 of ventricular myocytes in non-infarcted zone. RESULTS: Membrane capacitance was larger in HMI group than that in sham-operated group. Action potential duration was lengthened significantly in HMI group and early after depolarization (EAD) appeared in HMI group. The densities of I_to, I_K,tail and I_K1 were reduced significantly in HMI group (P<0.01), from (6.72±0.42) pA/pF, (1.54±0.13) pA/pF and (25.6±2.6) pA/pF in Sham-operated group to (4.03±0.33) pA/pF, (1.14±0.11) pA/pF and (17.6±2.3) pA/pF, respectively. CONCLUSION: The reduced densities of I_to, I_K,tail and I_K1 in ventricular myocytes of non-infarcted zone in HMI are responsible for the prolongation of APD and the presentation of EAD, which play important roles in the malignant arrhythmia of HMI.     

Effect of panax notoginseng saponins on electrophysiological characteristic of atrial cardiomyocytes in guinea pig

AIM: To study the effect of panax notoginseng saponins on the left atrial appendage (LAA) of the guinea pigs. METHODS: Standard microelectrode intracellular recording technique was used to record the LAA action potential (AP) and the effective refractory period (ERP) in the guinea pigs during the pouring with different density of PNS. RESULTS: The effect of PNS in concentration of 0.7, 7, 70, 700 mg/L was significant at 20 min, the APD50 and APD80 of the pouring at 20 min, 30 min, 40 min of the 70 mg/L was longer than the reference group (P<0.05). The rest potential (RP), action potential amplitude (APA) and Vmax kept no change during the pouring at 20 min with 4 difference densities from 0.7 to 700 mg/L. The pouring at 20 min of 7 mg/L and 70 mg/L obviously prolonged the ERP of the atrial cardiomyocytes. compared to the reference group, it prolonged from (127.00±7.26) ms to (153.00±9.19) ms and (161.00±10.21) ms (P<0.01). However, pouring at 10 min with 7 000 mg/L caused the arrhythmias. CONCLUSION: PNS prolongs the APD and ERP in guinea pig atrial cardiomyocytes. It may be the mechanism of PNS against arrhythmias in cellular level, which is similar to amiodarone.     

Effects of stretch on transient outward potassium and inward rectifier potassium current in cultured neonatal rat atrial myocytes

AIM：To investigate the effects of mechanical stretch on transient outward potassium current (Ito), inward rectifier potassium current (IK1) and action potential duration(APD) of cultured neonatal rat atrial myocytes. METHODS：Neonatal rat atrial myocytes were isolated and cultured on silicone sheeting with or without stretch for 24 h. The silicone membrane area was increased by 12% in stretched group. The cells without stretch served as control. Ito, IK1 and APD were recorded by the technique of whole-cell patch clamp. RESULTS：Compared with control group, Ito density in stretched myocytes was significantly reduced ［(16±04) pA/pF vs (121±29) pA/pF, P<001］, whereas IK1 density was increased ［(-108±08) pA/pF vs (-88±09) pA/pF, P<001］. The APDs at 50% and 90% levels of repolarization (APD50 and APD90) in the stretched cells were obviously decreased than those in non-stretched cells ［(105±14) ms vs (155±24) ms, (300±28) ms vs (563±36) ms, P<001］. CONCLUSION：Stretch stimulation leads to the reduction of Ito density, the increase in IK1 density and the shortness of APD in cultured rat atrial neonatal myocytes, which may contribute to atrial electrical remodeling induced by pressure overload.     

Zacopride enhances inward rectifier potassium current (IK1) to antagonize arrhythmias

AIM: To investigate the effects of zacopride on aconitine or BaCl2-induced arrhythmias and involved ionic mechanisms. METHODS: The whole-cell patch-clamp technique was used to record the inward rectifier K+ current (IK1), Ca+ current (ICa-L), Na+ current (INa), transient outward K+ current (Ito), the resting membrane potential (RMP) and action potential (AP) in the single cell of rat ventricular myocardium. Two arrhythmic models were elicited by injection of 30 μg/kg aconitine or 4 mg/kg BaCl2 intravenously. Zacopride at dose of 15 μg/kg was administered immediately after the development of first sinus rhythm disorders to observe its effects on arrhythmias. The ECGs were recorded simultaneously. RESULTS: In voltage clamp mode, 0.1-10.0 μmol/L zacopride dose-dependently enhanced IK1 with no significant effects on ICa-L, INa and Ito (P>0.05). Zacopride at concentration of 1.0 μmol/L showed the most potent activity on IK1 with approximately 30% increment both in inward current and outward current (P<0.01). Correspondingly, 0.1-10.0 μmol/L zacopride hyperpolarized RMP and shortened the action potential duration (APD) in a concentration-dependent manner (P<0.01). Furthermore, 1.0 μmol/L zacopride abolished aconitine-induced delayed afterdepolarization (DAD) and triggered activity (TA). In vivo, zacopride (15 μg/kg) significantly shortened the duration of arrhythmias elicited by aconitine ［from (57.58±3.21) min to (38.25±2.59) min］ or BaCl2 ［from (49.31±2.46) min to (30.94±1.73) min］. CONCLUSION: As an agonist of IK1, zacopride enhanced IK1, hyperpolarized RMP and shortened APD, which may be the fundamental mechanisms underlying its antiarrhythmic effect. Enhancing IK1 might be a new antiarrhythmic strategy.     

Effects of mechanical stretch on electrophysiological characteristics of calcium preconditioning myocardium

AIM: To investigate the effects of mechanical stretch under simulated anoxia and reoxygenation conditions on action potential (AP) and effective refractory period (ERP) of calcium preconditioning (CPC) in isolated papillary muscles of guinea pig hearts. METHODS: The intracellular standard glass microelectrode technique was used, and effects of stretch (intensity: 200 mg) on AP and ERP were recorded and observed in CPC papillary muscles. RESULTS: After stretching was implied during anoxia, the reductions of Vmax, RP, APA, APD50, ERP and APD90 in CPC group were less than those in anoxia-reoxygenation (AR) group, and the CT in CPC group was less elongated. Moreover, after the papillary muscles were stretched during reoxygenated reperfusion, the decreases in Vmax, RP, APA, APD50 and ERP in CPC group were less than those in AR group, and the CT and APD90 in CPC group were less extended. Streptomycin inhibited the effect of stretch on AP and ERP in CPC group. CONCLUSIONS: Under simulated anoxia and reoxygenation conditions, papillary muscles in CPC group may have better tolerance to the same stretch than those in the AR. Furthermore, streptomycin (a blockade of stretch-activated ionic channels) may inhibit the effect of mechanical stretch on action potential changes in CPC papillary muscles.     

Effect of hypercholesterolemia on the ionic currents in cardiac ventricular myocytes of rats

AIM: To determine whether chronic hypercholesterolemia affects ionic currents on cardiac ventricular myocytes of rats. METHODS: Whole-cell patch-clamp technique was used to record the ionic currents in single cardiac myocytes isolated from normal cholesterolemia and hypercholesterolemia rats. RESULTS: In the hypercholesterol group (group Ⅱ), serum total-cholesterol level was significantly higher than that of normal group (group Ⅰ) ［(3.10±0.62)mmol·L-1 vs (1.18±0.37)mmol·L-1, P<0.01, n=20］. The serum triglyceride content of group II was remarkably higher than that of group Ⅰ ［(1.51±0.30)mmol·L-1 vs (0.43±0.15)mmol·L-1, P<0.01, n=20］. In ventricular myocytes of rats, 50% repolarization of action potential duration (APD50) prolonged from (70.86±8.12)ms (group Ⅰ) to (116.16±6.90)ms (group Ⅱ) (n=10 in each group, P<0.01); APD90 prolonged from (95.10±7.27)ms (group Ⅰ) to (144.04±7.39)ms (group Ⅱ) (n=10 in each group, P<0.01); at the test potential of -120 mV, Ik1 increased from (-16.98±4.54) pA/pF(group Ⅰ) to (-19.92±4.08) pA/pF (group Ⅱ) (n=12 in each group, P<0.05); at the test potential of 0 mV, ICa-L decreased from (-8.56±1.29) pA/pF (group Ⅰ) to (-5.24±0.90) pA/pF (group Ⅱ) (n=10 in each group, P<0.01); at the test potential of +60 mV, Ito decreased from (13.20±1.97) pA/pF (group Ⅰ) to (10.30±1.97) pA/pF (group Ⅱ) (n=8 in each group, P<0.05). CONCLUSION: Hypercholesterolemia affects the ionic currents on cardiomyocytes of rats greatly, which may be the ionic mechanism of cardiac toxicity induced by hypercholesterolemia.     

Electrophysiological effects of amiodarone on pacemaker cells in guinea-pig left ventricular outflow tract under conditions of hypoxia,acidosis and treatment with epinephrine

AIM: To study the electrophysiological effects of amiodarone on the pacemaker cells in guinea-pig left ventricular outflow tract under the conditions of hypoxia, acidosis and treatment with epinephrine.METHODS: The action potentials of the pacemaker cells in guinea-pig left ventricular outflow tract were recorded by conventional intracellular microelectrode technique. The effects of amiodarone on the spontaneous slow response potentials were investigated under the conditions of hypoxia, acidosis and treatment with epinephrine.RESULTS: (1) Amiodarone at concentration of 0.1 μmol/L markedly decreased the rate of pacemaker firing (RPF) and maximal diastolic potential (MDP), lengthened 80% of the duration of action potential (APD80). Amiodarone at concentration of 1 μmol/L significantly decreased the velocity of diastolic depolarization (VDD) and RPF, the maximal rate of depolarization (Vmax), MDP and amplitude of action potential (APA), lengthened 50% of the duration of action potential (APD50) and APD80. Amiodarone at concentration of 10 μmol/L led to a significant decrease in VDD and RPF, Vmax, MDP and APA, a notable lengthening in APD50 and APD80 was also observed. (2) Under the condition of hypoxia and perfusion with deprived glucose content for 15 min, VDD, RPF, MDP, Vmax and APA decreased significantly, APD50 was shortened notably. Under the condition of hypoxia, amiodarone at concentration of 1 μmol/L significantly decreased VDD, RPF and Vmax, increased MDP, lengthened APD50 and APD80 as compared to the cells treated with hypoxia only. (3) Perfusion with pH 6.8 solution for 10 min, VDD and RPF significantly decreased, Vmax and APA notably reduced, APD80 was markedly shortened. Under the condition of acidosis for 10 min, amiodarone significantly decreased VDD, RPF, MDP and APA, lengthened APD50 and APD80 as compared to the cells under the condition of acidosis only. (4) Perfusion of epinephrine at concentration of 10 μmol/L for 10 min resulted in a significant increase in VDD, RPF, Vmax, MDP and APA, a notable shorting in APD50 and APD80 was also observed. Compared to 10 μmol/L epinephrine group, 1 μmol/L amiodarone+10 μmol/L epinephrine significantly reduced VDD, RPF, Vmax, MDP and APA, lengthened APD50 and APD80.CONCLUSION: Amiodarone markedly decreases the autorhythmicity of the pacemaker cells in guinea-pig left ventricular outflow tract. This electrophysiological effects were significantly influenced by hypoxia, acidosis and epinephrine.     

Effects of action potential duration restitution on ventricular arrhythmia in chronic heart failure rabbit hearts

AIM: To determine the effects of action potential duration restitution (APDR) on ventricular arrhythmia (VA) in Langendorff-perfused chronic heart failure (CHF) rabbit hearts. METHODS:Twenty male New Zea-land rabbits were equally divided into 2 groups randomly: control (CTL) group and CHF group. CHF was induced by abdominal aortic banding for 14 d. The echocardiography was applied to assess the cardiac function and structural change in both groups 4 weeks after the end of modeling. In the whole Langendorff-perfused hearts, the monophasic action potential (MAP) and the effective refractory period (ERP) were recorded and measured in ventricular chamber, and the action potential duration (APD) curves were also constructed in both groups. The burst pacing was used to induce APD alternans and VA. RESULTS: Compared with the same sites of CTL group, the 90% of MAP duration (MAPD90), the ERP, the maximal slope (Smax) of APDR curves were increased in CHF group (all P<0.05). The VAs in CHF group were easier to be induced than those in CTL group (all P<0.05). The coefficients of variation of Smax (COV-Smax) of APDR curves in CHF group were greater than those in CTL group (all P<0.05).CONCLUSION: Both Smax and COV-Smax of APDR curves increase during CHF to facilitate the ventricular arrhythmia.     

Activity of delayed rectifier potassium channel in alveolar macrophages from COPD rats

AIM: To explore the change of delayed rectifier potassium channel (KV) activity in alveolar macrophages (AM) in chronic obstructive pulmonary disease (COPD) rats. METHODS: COPD model was established by exposure of the animals to cigarette smoke. With whole-cell voltage- or current-clamp techniques, KV activity, membrane capacitance and resting membrane potential (Em) in AM from COPD model and control rats were compared. RESULTS: (1) Significant increases in total mononuclear cells and AM in bronchoal aveolar lavage fluid (BALF) were found in COPD group compared with in control group. (2) The AM KV current altitude in COPD group ［(520.5±38.7）pA， +50 mV, n=30］ was significantly lower than that in control group ［(713.6±44.4）pA， +50 mV, n=30， P<0.01］; (3) AM from COPD group had no significantly different capacitances (P>0.05), but had more positive Em (P<0.01) compared with those from control group. CONCLUSION: Inhibition of KV function, increase in excitability and more positive Em in AM from COPD rats may be involved in the AM contribution to the COPD development.     

Effect of platelet activating factor on the action potential and potassium currents in guinea-pig ventricular myocytes

AIM: To investigate the effects of platelet activating factor (PAF) on the action potential and potassium currents in guinea-pig ventricular myocytes. METHODS: By using whole-cell patch clamp technique, the effects of PAF on APD₉₀, I_K1 and I_K were investigated in enzymatically dispersed single guinea-pig ventricular myocytes. RESULTS: With 5 mmol/L ATP in the pipette electrode, 1 μmol/L PAF increased APD₉₀ from (225.8±23.3) ms to (352.8±29.8) ms (n=5, P<0.05), decreased I_K1 and I_K tail currents from (-6.1±1.3) nA to (-5.6±1.1) nA (n=5, P<0.05) at -120 mV and from (173.5±16.7) pA to (152.1±11.5) pA (P<0.05, n=4) at +30 mV, respectively. In contract, without ATP in the pipette electrode, 1 μmol/L PAF shortened APD₉₀ from (153.0±24.6) ms to (88.2±19.4) ms (n=5, P<0.01). Incubation of myocytes with 1 μmol/L glibenclamide, a blocker of I_KATP restored prolongation of APD induced by PAF. CONCLUSION: In guinea-pig ventricular myocytes, with 5 mmol/L ATP in the pipette, PAF prolonged APD partly due to the inhibition of I_K and I_K1, while with 0 mmol/L ATP in the pipette, PAF induced an activation of I_KATP, hence a decrease in APD was observed. Therefore, PAF might amplify the heterogeneity between ischemia and normal cardiac myocytes during ischemic reperfusion, which might play a vital role in the pathogenesis of the arrhythmias induced by ischemia/reperfusion.     

Effects of simvastatin on transient outward potassium current in ventricular myocytes of normocholesterolemic rabbits suffering from ischemia and reperfusion

AIM: To investigate the effects of simvastatin on transient outward potassium current (Ito) in left ventricular myocytes of rabbit heart undergoing ischemia-reperfusion, so as to explore the cellular (ionic) mechanism of statin treatment for antiarrhythmia. METHODS: Forty-five rabbits were randomly divided into three groups: ischemic-reperfusion group (I-R), simvastatin intervention group (statin) and sham-operation control group (sham). Anesthetized rabbits were subjected to 30 min ischemia by ligation of the left anterior descending coronary artery and 60 min reperfusion after oral administration of simvastatin at dose of 5 mg·kg-1·d-1(statin group) or placebo (I-R group) for 3 d. Single ventricular myocytes were isolated enzymatically from the epicardial zone of the infracted region derived from the hearts in I-R, statin group and the same anatomy region in sham. Whole cell patch clamp technique was used to record Ito. Simultaneously, the level of serum cholesterol was examined. RESULTS: No significant difference in serum cholesterol concentration among three groups was observed. The Ito current density (at +60 mV) was significantly decreased in I-R ［(9.49 ±1.91) pA/pF, n=11］ compared with sham ［(17.41± 3.13) pA/pF, n=15, P＜0.01］ and statin ［(15.24 ± 2.41) pA/pF, n=11, P＜0.01］, although there was slight reduction in statin group compared with sham (P＜0.05). CONCLUSION: Ischemia-reperfusion induces significant down-regulation of Ito, which may underlie the altered electrical activity and prolong abnormal transmembrane action potential duration of the surviving ventricular myocytes. Pretreatment with simvastatin attenuates these changes without lowering the serum cholesterol level, suggesting that simvastatin may reverse this electrical remodeling, thus contributing to the ionic mechanism of statin treatment for antiarrhythmia.     

Effects of tanshinone IIA on cardiac monophasic action potential in acute cerebral ischemia rats

AIM: To investigate the effects of tanshinone IIA (Tan) on cardiac action potential in rats with acute cerebral ischemia (ACI). METHODS: ACI was established in rats accordingly. Animals were divided into 3 groups:sham group, ACI group, and ACI with Tan treatment group. The defect of neural function in each group was graded, electrocardiogram was measured, monophasic action potential was recorded, and the levels of cardiac troponin I (cTnI) and creatine kinase-MB (CK-MB) were examined by commercially available kits. RESULTS: Compared with ACI group, Tan significantly decreased the scores of the defect of neural function, reduced the incidence and duration of the abnormalities in electrocardiogram, prolonged the effective refractory period, action potential duration at 50% repolarization and action potential duration at 90% repolarization, and inhibited the elevation of cTnI and CK-MB levels. CONCLUSION: Tan maintains a stable heart rhythm in ACI rats, which may be related to its protective effect on ischemic myocardium.     

Electrophysiological changes in rat ventricular myocardium at different stages of experimental diabetes

AIM: To explore the probable mechanisms of diabetes-induced arrhythmias. METHODS: Diabetes was induced in male SD rats, using a single injection of alloxan into tail vein. Untreated age-matched animals were used as controls. All animals were observed by 2, 4, 6 and 8 weeks, respectively. Transmembrane potentials were recorded with conventional glass microelectrodes. RESULTS: Action potential duration(APD) at all level (APD10, APD20, APD30, APD50, APD70, APD90) was significantly lengthened in right ventricular papillary muscle from week 2 of diabetes. At week 8, APD was more lengthened at any level of repolarization than that at week 2. No differences were observed in the maximum rate of depolarization(V_max), overshoot(OS) and action potential amplitude(APA) as well as the resting membrane potential(RP) from the 2th to 8th week of diabetes. CONCLUSION: The results indicate that prolongation of APD may be prominently responsible for the increased incidence of cardiac re-entry-arrhythmias and sudden death, especially at late stages of diabetes.     

Electrophysiological effects of lidocaine on myocardial tissue in guinea-pig left ventricular outflow tract under conditions of hypoxia,acidosis and treatment with epinephrine

AIM：To study the electrophysiological effects of lidocaine on the myocardial tissue in guinea-pig left ventricular outflow tract under the conditions of hypoxia, acidosis and treatment with epinephrine. METHODS：The action potentials of pacemaker cells in guinea-pig left ventricular outflow tract were recorded by conventional technique with intracellular microelectrodes. The effects of lidocaine on the spontaneous slow response potentials were investigated under the conditions of hypoxia, acidosis and treatment with epinephrine (EPI). RESULTS：Lidocaine markedly decreased the rate of pacemaker firing (RPF), the velocity of diastolic depolarization (VDD), the maximal rate of depolarization (Vmax), the maximal diastolic potential (MDP) and the amplitude of action potential (APA). Lidocaine also shortened the 50% and 80% of duration of action potential (APD50 and APD80). At the concentrations from 0.1 μmol/L to 10 μmol/L, the effects of lidocaine were more significant. Under the condition of hypoxia and perfusion with deprived glucose content for 15 min, VDD, RPF, Vmax, MDP and APA significantly decreased, and APD50 notably shortened. Under the condition of hypoxia, lidocaine at 1 μmol/L significantly decreased VDD, RPF, Vmax and APA as compared with the cells treated with hypoxia only. Perfusion with pH 6.8 solution for 10 min, VDD, RPF, Vmax and APA significantly decreased, MDP notably increased, and APD50 and APD80 markedly shortened. Under the condition of acidosis for 10 min, lidocaine significantly decreased VDD, RPF and Vmax, and lengthened APD50 and APD80 as compared with the cells under the condition of acidosis alone. Perfusion with EPI at 10 μmol/L for 10 min resulted in significant increases in VDD, RPF, Vmax, MDP and APA, and notable shortenings of APD50 and APD80 were also observed. Compared with 10 μmol/L EPI group, 1 μmol/L lidocaine+10 μmol/L EPI significantly reduced VDD, RPF, MDP and APA, and lengthened APD50 and APD80. CONCLUSION：Lidocaine markedly decreases the autorhythmicity of the pacemaker cells in guinea-pig left ventricular outflow tract and influences the electrophysiological effects of hypoxia, acidosis and EPI.     

Mechanism of arrhythmias caused by autoantibodies against β1-adrenoceptors induced by hepatitis B virus in mice

AIM: To investigate the significance of autoantibodies against β1-adrenoceptors induced by hepatitis B virus in the pathogenesis of hepatitis virus myocarditis. METHODS: 30 mice were injected peritoneally with an emulsion of hepatitis B virus and complete Freund's adjuvant every three weeks. The autoantibodies were examined by ELISA, the heart and liver specimens were collected on 56 d for pathological observation and the binding of the autoantibodies to guinea pig cardiac myocytes were examined by immunofluorescence. Using the patch clamp technique, the effects of 1∶50 autoantibodies purified by octanoic acid extraction on the action potential and L type Ca2+ currents of guinea pig cardiac myocytes were also investigated. RESULTS: There was a good correlation between the autoantibodies and hepatitis B virus. Without pathological changes in the heart and liver specimens, 6 mice of the test group manifested bundle branch block, sinus arrest and premature ventricular beat etc, which were positive in the autoantibodies. The specific binding of the autoantibodies of the mice to guinea pig cardiac myocytes was observed. 1∶50 autoantibodies of the mice prolonged APD20, APD50, APD90 by 36.46%, 29.63% and 12.40%, respectively and enhanced L type Ca2+ currents by (49.67±16.01)%. CONCLUSIONS: Autoantibodies against β1-adrenoceptors of the mice induced by hepatitis B virus result in several arrhythmias, which might be mediated by the enhancement of L type Ca2+ currents.     

Characteristics of transient outward potassium current in repolarization 1 phase from the canine right ventricular mid-myocardial cells

AIM: To examine the electrophysiological characteristics of transient outward potassium current(Ito₁) in repolarization 1 phase from the canine right ventricular M cells. METHODS: By use of whole cell patch-clamp technique, we quantitatively researched the ionic intensity, density of Ito₁ and the notch magnitude of action potential in repolarization 1 phase. RESULTS: (1) The activating process of Ito₁ of canine right ventricular M cells presented evident voltage-dependency. Under the condition of 37℃, 5 000 ms, 0 mV and +70 mV, the average peak Ito₁ intensity of right ventricular M cell were (690±380) pA and (3 130±1 910) pA, respectively (P＜0.01). (2) The Ito₁ intensity of canine right ventricular M cell possessed obvious frequent dependency. Under the condition of 37℃,+70 mV, 500 ms and 5 000 ms, the average peak Ito₁ intensity were (1 690±830) pA,(3 130±1 910) pA, respectively(P＜0.01), corresponding to the increase of action potential "spike-dome" magnitude in repolarization 1 phase. CONCLUSION: Potent Ito₁ as well as the "spike-dome"-like action potential figure mediated by Ito₁ is one of the prominent electrophysiological characteristics of the canine right ventricular M cells.     

Effects of cardiac remodeling on atrial arrhythmogenesis in aged rabbit left atrium

AIM: To investigate the effects of myocardial remodeling of aged left atrium (LA) on atrial arrhythmogenesis in rabbits.METHODS: The male New Zealand rabbits were divided into young LA and aged LA groups. By observing the changes of monophasic action potential (MAP) and burst-pacing in LA of the rabbits in vivo, the main cardioelectrophysiological parameters such as resting membrane potential (RMP), action potential amplitude (APA), ma-ximum rise veloctiy of action potential (dv/dt_max), plateau potential and action potential duration at 30%, 50% and 90% (APD₃₀, APD₅₀ and APD₉₀), as well as the inducibility and duration of atrial arrhythmias were recorded. L-type calcium current (I_Ca,L) was analyzed via whole-cell patch-clamp technique in enzymatically dissociated single rabbit LA myocytes. The myocardial collagen content was quantified after Masson staining, and the ultrastructure of the LA cells was observed under scanning electron microscope. The expression of Cav1.2 in LA tissue of the 2 groups was detected by Western blot.RESULTS: Compared with young LA group, dv/dt_max and plateau potential were significantly decreased, APD₃₀ and APD₅₀ were shortened, and APD₉₀ was notably prolongated in aged LA group (P<0.01). The inducibility or duration of atrial arrhythmias was severely increased or prolongated in aged LA group (P<0.01). With voltage clamp model, the density of I_Ca,L in aged LA group was significantly decreased, and current-voltage curve was notably moved upward compared with young LA group. When the clamp potential was +20 mV, the density of I_Ca,L was notably modified from (11.72±1.39) pA/pF in young LA group to (6.08±0.98) pA/pF in aged LA group (P<0.01). Compared with young LA group, the protein level of collagen was significantly increased (P<0.01), and the arrange of atrial myocytes was irregular in LA of rabbits in aged LA group. The atrial myocytes of the LA wall in aged LA group exhibited abnormal ultrastructural alterations, such as karyopyknosis, irregular and swelling mitochondria with the presence of vacuoles, and mild and severe sarcomere degeneration. Compared with those in LA tissues of young rabbits, the expression levels of Cav1.2 in the LA tissues of aged rabbits were severely reduced (P<0.01), and had a significant positive correlation with the reduction of I_Ca,L (r=0.83, P<0.01).CONCLUSION: The pathophysiological characteristics of aged LA are significantly altered, and might contribute to vulnerability and susceptibility of occurrence of atrial fibillation in aged rabbits. The mechanisms might completely attribute to the notable reduction of I_Ca,L, abnormal alterations of ultrastructures and obvious decrease in the expression of Cav1.2 in the aged LA of aged rabbits.     

Effects of endogenous nitric oxide on potassium channels of bronchial smooth muscle cells from asthmatic rats

AIM: To investigate the effects of in vivo application of L-arginine on potassium channels in bronchial smooth muscle cells (BSMC) isolated from asthmatic model rats. METHODS: Male SD rats were randomly divided into control group, asthmatic group and asthmatic rats treated with L-arginine (L-Arg group). Single BSMCs were obtained by acute enzyme separation method. The resting membrane potential (Em), Ca2+-activated K+ channels (BKCa) currents and voltage-dependent K+ channel (Kv) currents in BSMCs were recorded under whole-cell patch clamp technique. RESULTS: (1) The Em of asthmatic group was significantly lower than that in control group (P<0.05). In vivo application of L-Arg significantly hyperpolarized BSMCs near to control group (P>0.05). (2) The peak current density at +50 mV of KCa: IKca in asthmatic group ［(43.8±16.5) pA/pF］ was significantly lower than that in normal group ［(72.5±19.9) pA/pF］ (P<0.01). Treatment with 300 mg/kg L-Arg significantly increased IKca in asthmatic group to (58.7±12.4) pA/pF (P<0.05). (3) The peak currents density at +50 mV of Kv: IKv in asthmatic group ［(32.4±8.7) pA/pF］ was significantly lower than that in control group ［(57.7±9.8) pA/pF］ (P<0.01). Treatment with L-Arg also significantly increased IKv in asthmatic group to (43.6±7.9) pA/pF, (P<0.05). CONCLUSION: Endogenous NO improves Em in asthmatic BSMCs, increases the activities of BKCa channels and Kv channel. These findings implicate that NO may have a potential therapeutically role in airway hypersensitivity.     

Effects of catestatin on calcium handling abnormalities and ventricular arrhythmia after myocardial infarction in rats

AIM: To determine the effects of catestatin (CST) on calcium handling abnormalities and ventri-cular arrhythmia (VA) after myocardial infarction (MI) in rats. METHODS: The adult male SD rats (n=85) were randomly divided into sham group (n=20) and operation group (n=65). MI was induced by ligation of the left anterior descending coronary artery in operation group. The rats in sham group underwent pericardiotomy but without ligating the artery. The rats survived for 1 week after operation were randomly assigned to MI group and CST group. The rats in CST group was treated with CST (30 mg·kg^-1·d^-1, intraperitoneal administration) for 4 weeks, while saline was applied to the rats in sham group and MI group. The calcium imaging study was performed by loading isolated ventricular cardiomyocytes with Fura-2 AM. In the whole Langendorff-perfused hearts, the programmed electrical stimulation was used to induce action potential duration (APD) alternans and VA. The protein levels of ryanodine receptor 2 (RyR2), phosphorylated RyR2 (p-RyR2), calcium/calmodulin-dependent protein kinase II (CaMKII) and phosphorylated CaMKII (p-CAMKII) were determined by Western blot. RESULTS: Compared with sham group, the protein levels of p-RyR2 and p-CaMKII, the diastolic intracellular Ca²⁺ concentrations and the inducibility of VA were significantly increased, whereas the thresholds of Ca²⁺ transient (CaT) and APD alternans and the CaT amplitude were markedly decreased in MI group (P<0.01). Compared with MI group, the protein levels of p-RyR2 and p-CaMKII, the diastolic intracellular Ca²⁺ concentration and the inducibility of VA were significantly decreased, while the thresholds of CaT and APD alternans and the CaT amplitude were markedly increased in CST group (P<0.01). No significant difference of the protein expression of RyR2 and CaMKII among the 3 groups was observed (P>0.05). CONCLUSION: CST reduces the susceptibility to VA after MI via preventing calcium handling abnormalities.