Effect of interleukin-2 on intracellular calcium levels in rat ventricular myocytes during anoxia and reoxygenation

AIM: To investigate the effect of interleukin-2(IL-2) on the intracellular calcium in electrically stimulated adult rat ventricular myocytes during anoxia and reoxygenation. METHODS: The isolated cardiac ventricular myocytes were exposed to 5 min anoxia followed by 10 min reoxygenation. Chemical anoxia was introduced by Krebs-Henseleit(K-H) solution containing 10^-3 mol/L sodium dithionite. The spectrofluorometric method was used to verify intracellular calcium transient with fura-2/AM as calcium fluorescence probe. RESULTS: It was shown that during anoxia, the amplitude of Ca²⁺ transient was decreased, diastolic [Ca²⁺]_i, time to peak and time to relaxation of Ca²⁺ transient were increased. All the parameters were got back but did not returned to the pre-anoxia level during reoxygenation. IL-2 at 2×10⁵ U/L administrated during anoxia aggravated the effect of rexoxygenation on [Ca²⁺]_i transient. Pretreatment with a specific κ opioid antagonist, nor-BNI(10^-8 mol/L), abolished the effect induced by IL-2 during anoxia on the [Ca²⁺]_i transients, whereas specific δ opioid antagonist, naltrindole(10^-6 mol/L), did not cancel the effect. CONCLUSION: It is concluded that administration of IL-2 during anoxia aggravated the effect of reoxygenation on the [Ca²⁺]_i transients of isolated ventricular myocytes, which was mediated by cardiac κ opioid receptor pathway.     

Interleukin-2 altered the frequency -dependent relationship of intracellular calcium in rat ventricular myocytes

AIM:We examined the effect of interleukin-2 (IL-2) on calcium handling of rat cardiomyocytes. METHODS:The effects of steady state and transient changes in stimulus frequency on the intracellular calcium transient were investigated in the isolated ventricular myocytes with spectrofluorometry technique. RESULTS: Under the steady state (0.2 Hz), IL-2 at 2×10⁵U/L decreased the peak [Ca²⁺] i and amplitude of the [Ca²⁺]i transient, increased the diastolic calcium level, and prolonged the decay of the calcium transient. At 1.25 mmol/L of extracellular [Ca²⁺], when increasing the stimulus frequency from 0.2 to 1.0 Hz, diastolic calcium level and peak [Ca²⁺] i as well as the amplitude of the transient were increased. The positive frequency relationship was blunted in the IL-2-treated myocytes and this was not normalized by increasing extracellular [Ca²⁺] to 2.5 mmol/L. The caffeine induced Ca²⁺ release was increased with increase in stimulus frequency. IL-2 inhibited the frequency relationship of caffeine induced Ca²⁺ release. The restitution was not different between control and IL-2 groups at the 1.25 mmol/L of extracellular [Ca²⁺], which was slowed in IL-2-treated myocytes when the extracellular [Ca²⁺] was increased to 2.5 mmol/L. CONCLUSIONS:It is concluded that the blunted frequency response of IL-2-treated myocytes was resulted from the decrease in SR Ca²⁺ release, which was related to depression of SR function. Despite the evidence of depressed SR Ca²⁺ uptake, the restitution of calcium transient at 1.25 mmol/L of extracellular remains unchanged, which maybe due to the increase in the Na⁺/Ca²⁺ exchanger activity.     

Role of calcium ion in the cyotoxicity and DNA fragment induction in HL-60 cells by 6F isolated from Pteris semipinnata L.

AIM: To investigate the changes of cytosolic free calcium concentration([Ca²⁺]_i) and expression of Bcl-2 in HL-60 cells treated by 6F isolated from Pteris semipinnata L.(PSL), and to discuss the relations between calcium ion and cytotoxicity and DNA fragment induction effects of 6F. METHODS: HL-60 cells were used as in vitro model. [Ca²⁺]_i was measured on fluorescent spectrophotometry using Fura-2/AM as Ca²⁺ indicator. Bcl-2 expressing level was measured by flow cytometry. Tetrazolium salt(MTT) and diphenylamine staining methods were applied for cytotoxicity assay and DNA fragmentation detection, respectively. RESULTS: [Ca²⁺]_i increased obviously in a dose and time dependent manner after treated HL-60 cells with 6F. 6F decreased the expressing level of Bcl-2. Adding 2 mmol/L Ca²⁺ to the medium, or 1 mmol/L EDTA to chelate Ca²⁺, or 4 μmol/L calcium ionophore A 23187 to increase the concentration of cytosolic Ca²⁺, the DNA fragment induction by 6F was not affected, whereas the cytotoxicity of 6F was enhanced. 250 μmol/L Zn²⁺ attenuated the DNA fragment induction, and the cytotoxicity of 6F against HL-60 cells was enhanced significantly. CONCLUSION: It was speculated that the decreased expressing of Bcl-2 by compound 6F was related to increased [Ca²⁺]_i in HL-60 cells, and DNA fragment induction was possibly catalyzed by Ca²⁺ - independent DNase.     

Alteration of myocardial sarcoplasmic reticulum Ca2+ transport protein expression in neonatal hypothyroid rats

AIM: To investigate the alteration of sarcoplasmic reticulum (SR) Ca²⁺ transport proteins including sarcoplasmic reticulum Ca²⁺-ATPase 2a(SERCA2a) and phospholamban(PLB) mRNA expression as well as the alteration of myocardial SR Ca²⁺-ATPase activity in neonatal hypothyroid rats, and to explore the effect of levothyroxine(L-T₄) substitution therapy on the above indexes.METHODS: Hypothyroidism was induced by the administration of propylthiouracil (PTU, 50 mg/d) to the pregnant SD rats by gavage beginning on embryonic day 15 and continuing throughout the lactational period. A subgroup of neonatal hypothyroid rats were intraperitoneally injected with L-T₄ levothroxine (20 μg/kg BW daily), starting from the day of birth. Other pregnant SD rats received normal saline instead of PTU. The samples of the rats in all 3 groups were harvested at postnatal day 3, 5 and 7 respectively (n=10). After measurement of serum thyroid hormone levels, the hearts were removed and the ventricles were weighed (HW). The concentration of calcium in ventricular myocardium(ventricular myoCa²⁺) was detected by fluorospectrophotometry and the activity of SR Ca²⁺-ATPase was determined by the inorganic phosphorus method. The mRNA expression of SERCA2a and PLB was also detected by real-time PCR. RESULTS: Neonatal hypothyroid rats had a significant lower level of SERCA2a mRNA (P<0.05) and a higher level of PLB mRNA (P<0.01), and subsequent lower SERCA2a/PLB at each postnatal day (P<0.01) was observed. Compared with hypothyroid group, the mRNA expression of SERCA2a significantly increased (P<0.05) and that of PLB significantly decreased (P<0.05) in L-T₄ treatment group. The concentration of ventricular MyoCa²⁺ in hypothyroid group was significantly higher than that in control group (P<0.01), and that in L-T₄ treatment group showed a significant decrease as compared with hypothyroid group (P<0.05). The activity of sarcoplasmic reticulum Ca²⁺-ATPase in hypothyroid group was significantly lower than that in control group (P<0.01), and that in L-T₄ treatment group showed a significant increase as compared to hypothyroid group (P<0.05). CONCLUSION: The deficiency of thyroid hormone, resulting in decreased expression of SERCA2a mRNA as well as increased PLB mRNA, contributes to the reduction of SR Ca²⁺-ATPase activity in neonatal rats. This may be one of the most important mechanisms of myocardial systolic and diastolic dysfunctions.     

Effects of glucose and Mg2+ in the neurons damaged by glutamate

AIM and METHODS: To observe the effects of glucose-free and Mg²⁺-free in the extracellular fluid on the changes of [Ca ²⁺]_i in the cerebro-cortical neurons damaged by 1mmol/L glutamate using laser confocal scanning microscope. RESULTS: Both frequency and amplitude of neuronal calcium oscillation induced by glutamate were lowered in glucose-free and Mg²⁺-free buffers. The basic [Ca²⁺]_i concentration was lowered in the former case , but it was elevated in the latter case. CONCLUSION: Mg²⁺-free aggravates [Ca²⁺]_i overload induced by 1mmol/L glutamate ,under certain conditions the glucose-free might resist damage role of glutamate and Mg²⁺-free.     

Changes of myocardial nuclear membrane Ca2+-ATPase function in ischemia/reperfusion injury

AIM: The changes of myocardial nuclear membrane Ca²⁺ -ATPase function was investigated in ischemia/reperfusion injury. METHODS: The model of myocardial ischemia/reperfusion injury was established in rats. Myocardial nuclei were purified with sucrose density centrifugation, the activity of Ca²⁺ -ATPase was measured and calcium uptake was assayed with [⁴⁵ Ca²⁺ ] . RESULTS: Plasma levels of malondialdehyde (MDA) and free fatty acid (FFA) in myocardial ischemia/reperfusion injury increased significantly( P<0.01 vs control). Ca²⁺ -ATPase activity and [⁴⁵ Ca²⁺ ] uptake was lower than normal at below 10 μmol/L, while higher at 50 μmol/L. CONCLUSION:These data indicate dysfunction of nuclear menbrane calcium pump and [⁴⁵ Ca²⁺ ] uptake function in myocardial ischemia/reperfusion injury.     

Salvia miltiorrhiza antagonized the alterations of contraction and intracellular calcium of rat ventricular cardiomyocytes induced by anoxia and reoxygenation

AIM:To study the effect of salvia miltiorrhiza (SM) on cell contraction and intracellular calcium of enzymatically isolated rat ventricular myocytes during normoxia and anoxia/reoxygenation.METHODS:Contraction and intracel ular calcium were determined with video tracking system and spectrofluorometric method,and the chemical anoxic method was employed. RESULTS:The ±dL/dt_max, dL of cell contraction and the amplitude of [Ca²⁺]_i in the cardiomyocytes following SM treatment were decreased in a dose-dependent manner. During anoxia, the ±dL/dt_max, dL and amplitude of [Ca²⁺]_i were decreased, while the diastolic Ca²⁺ level was elevated compared with control group. All the contractile parameters and the diastolic Ca²⁺ level were back toward pretreatment values during reoxygenation, but could not return to control level. After the treatment with SM (3 g/L), ±dL/dt_max and dL of cell contraction and the amplitude of [Ca²⁺]_i were higher and the diastolic Ca²⁺ level was lower than those in anoxia/reoxygenation group. CONCLUSION:SM antagonized effects of anoxia and reoxygenation on cell contraction and intracellular calcium in isolated ventricular myocytes.     

Intracellular calcium alterations induced by endotoxin and IL-1β in rabbit hypothalamic neurons

AIM: To investigate intracellular free calcium ( [Ca²⁺]i ) alterations in hypothalamus of febrile rabbits induced by endotoxin (ET), and compare with the effect of ET and IL-1β on i in hypothalamic neurocytes from normothermia rabbits. METHOD: The concentration of [Ca²⁺]i was determined by using spectrofluorometer and fluorescent Ca²⁺ probe fura-2 /Am. RESULTS: 1. A minute dose of ET (2 ng/mL) induced a significant rise in [Ca²⁺]i in hypothalamic neurocytes from normothermia rabbits. The rise in [Ca²⁺]i in hypothalamic neurocytes from febrile rabbits induced by intravenous injection of ET was also observed. 2. In hypothalamic neurocytes from normotheria rabbits, IL-1β failed to affect [Ca²⁺]i at concentrations of 100, 500, 1 000ng/mL, respectively. CONCLUSION:The action site of low concentration of calcium that plays a regulatory role during fever seems unlikely to be in cytosolic compartment of hypothalamic neurons. The change of [Ca²⁺]i in hypothalamic neurocytes by ET can not be considered the direct effect of IL-1β.     

Effects of fructose-1,6-diphosphate on adriamycin-induced calcium and sarcoplosnic reticulum Ca2+-ATPase activity in cardiomyocytes of rats

AIM: To study the effects of fructose-1,6-diphosphate (FDP) on adriamycin (ADR)-induced calcium and sarcoplasmic reticulum Ca²⁺-ATPase activity in cardiomyocytes of rats. METHODS: Rats were treated with ADR by intraperitoneal injection (2.5 mg·kg^-1 body weight) once every two days for 11 days, and then ADR-treated rats were intervened by FDP at different dosages (ip) once every other day for 41 days. Enzyme linked immune absorption assay (ELISA) was employed to detect froponin I (CTnI). CK-MB was examined by monoclonal antibody. Intracellular free calcium concentration was measured on fluorescent spectrophotometry and SRCa²⁺-ATPase activity was examined by inorganic phosphate. RESULTS: FDP (300, 600, 1 200 mg·kg^-1) significantly reduced the levels of CTnI and CK-MB in serum. Decreased calcium and increased SRCa²⁺-ATPase activity in cardiomyocytes were also observed when ADR-treated rats were intervened by FDP (P＜0.01). CONCLUSION: FDP reduced the injury of cardiotoxicity induced by ADR via decreasing intracellular free calcium and increasing SRCa²⁺-ATPase activity in cardiomyocytes.     

Expression of calcium handling protein in diastolic heart failure

AIM:To elucidate molecular mechanisms underlying calcium handling protein in diastolic heart failure (DHF) from mRNA level and protein expression, including calcium adenosine triphosphatase (Ca²⁺-ATPase), phospholamban, ryanodine receptor, calsequestrin and L-type calcium channel.METHODS:The mRNA of these calcium handling genes were detected by RT-PCR, and the protein levels were analyzed by Western blot analysis.RESULTS:Compared with sham-operated rabbits, the steady-state levels of mRNA encoding the SR Ca²⁺-ATPase and cardiac L-type calcium channel were decreased significantly in rabbits with DHF, and protein level of SR Ca²⁺-ATPase was greatly reduced, whereas the mRNA and protein levels of other calcium handling protein were unchanged.CONCLUSION:L-type calcium channel and the sarcoplasmic reticular Ca²⁺-ATPase were down regulated in DHF. These changes may be a contributory factor for DHF.     

Alteration of cardiac sarcoplasmic reticulum function in vitamin D3-induced calcium overload rats

AIM:To study alterations of cardiac sarcoplasmic reticulum (SR) function in vitamin D₃-induced calcium overload rats. METHODS: The Ca-overload rat models were prepared by vitamin D₃ plus nicotine. Cardiac SR was seperated by centrifuging. The measurement of SR Ca²⁺uptake and Ca²⁺ release activities were preformed by the Millimore filtration technique. Specific SR -ryanodine binding capacity was measured by radioligand method. RESULTS: Compared with control,myocardial calcium content in calcium overload rats increased by 78%(P＜0.01), SR Ca²⁺ uptake and Ca²⁺ release activities decreased by 64% and 40% respectively(P＜0.01),and in the meantime ,the Ca²⁺-ATPase activity decreased by 65%(P＜0.01).Maxmum value for -ryanodine binding decreased by 51%(P＜0.01). CONCLUSION:The function of cardiac SR in calcium-overload rats was decreased.     

Foam cell formation and intracellular Ca2+ alteration

AIM:These studies aimed at exploring the alteration of intracellular Ca²⁺ level in the course of macrophage-derived foam cell formation as well as its mechanism.METHODS:Foam-like cell was generated by peritoneal macrophage of C57BL/6J mouse, which is susceptible to atherosclerosis, incubated in 10 mg·L^-1 oxidized low density lipoprotein for 96 hours. With the technique of Ca²⁺ fluorescent indicator and the assay of NADH-oxidizing coupling spectrum-alteration, the intracellular Ca²⁺ level and membranous Ca²⁺-ATPase activity of the above foam-like cell were determined.RESULTS:The foam-like macrophage Ca²⁺ level was 2.7 times higher than the control macrophage, and the former Ca²⁺-ATPase activity was 24% of the later.CONCLUSION:The results suggested that macrophage-derived foam cell formation was connected with slow Ca²⁺ entry or release, which possibly derived from long-lasting opening of membranous Ca²⁺ channels at the early stage and irreversible inactivating of membranous Ca²⁺ pump at the late stage.     

Roles of ERKs and intracellular free calcium in cardiomyocyte hypertrophic response induced by endothelin-1

AIM: To study the roles and mechanisms of ERKs and intracellular free calcium in cardiomyocyte hypertrophic response induced by endothelin-1(ET-1). METHODS: (1) Neonatal rat cardiomyocyte hypertrophic response was assayed by measuring cell surface area and protein content; (2) ERKs activity was determined by Whatman Paper Filter method; (3) Intracellular free calcium concentration ([Ca²⁺]i) was measured using Fura-2/AM as a fluorescent indicator. RESULTS:(1)ET-1 could increase total protein production,surface area,ERKs activity and[Ca²⁺]i in cultured cardiomyocyte in dose-dependent manner at concentrations ranging from 10^-9to 10^-7mol/L.And this effect could be abolished by BQ123,an antagonist of ETA receptor,partly inhibited by PTX,but not by BQ788,an antagonist of ETB receptor.(2)The activation of ERKs and the increase of[Ca²⁺]i induced by ET-1 were obviously in hibited by PD98059,a selective ERKs kinase inhibitor,and nifedipine,a calcium channel blocker,respectively.Both antagonists partialy inhibited ET-1-stimulated cardiomyocyte hypertrophic response.(3)Staurosporine,a selective PKC inhibitor,could inhibit ET-1-stimulated cardiomyocyte hypertrophic response and increase of[Ca²⁺]i,but not af ect the activation of ERKs.CONCLUSION: Cardiomyocyte hypertrophic response induced by ET-1 is mediated by ET_A receptor coupled to PTX-sensitive G-protein, which involves at least two signalling pathways: PKC-mediated increase of [Ca²⁺]i , and PKC-independent activation of ERKs.     

Role of potassium channels in the regulation of intracellular free Ca2+ concentration of pulmonary artery smooth muscle cells in rats

AIM: To investigate the role of potassium channels in the regulation of intracellular free calcium concentration ( [Ca²⁺]_i) of pulmonary artery smooth muscle cells (PASMCs) in rats. METHODS: The fluorescence Ca²⁺ indicator Fura-2/AM was used to observe [Ca²⁺]_i of rat PASMCs in normal and chronic hypoxic condition. The influences of potassium channels on PASMCs proliferation were assessed by MTT assay. RESULTS: 1. In normoxic condition, [Ca²⁺]_i was (156.91±8.60) nmol/L, and in hypoxic condition, [Ca²⁺]_i was (294.01±16.81) nmol/L. 2. In normoxic condition, the voltage-dependent K⁺-channel antagonist 4-aminopyridine (4AP), but not the Ca²⁺-activated K⁺-channel antagonist tetraethylammonium (TEA) and the ATP-sensitive K⁺-channel antagonist glibenclamide (Glib) increased [Ca²⁺]_i. 3. In hypoxic condition, 4AP and TEA caused the rise in [Ca²⁺]_i , but Glib had no effect on [Ca²⁺]_i. 4. MTT assay showed that 4AP increased the value of absorbing light degree (A value) in normoxic and hypoxic condition (0.582±0.062,0.873±0.043,respectively, P＜0.01), TEA increased A value only in hypoxic condition, and Glib had no effect on the proliferation of PASMCs. CONCLUSIONS: K_V plays an important role in the regulation of [Ca²⁺]_i and proliferation of PASMCs. K_Ca serves as distinct responsive roles in the regulation of proliferation of PASMCs in hypoxic condition. K_ATP has no effect on [Ca²⁺]_i and proliferation of PASMCs in normoxic and hypoxic conditions.     

ATPase activities and Ca2+/calmodulin alterations in hippocampi of rats with PTSD-like behaviors

AIM: To explore the pathophysiological bases in the pathogenesis of the lasting emotional behavioral disorders following posttraumatic stress disorder(PTSD). METHODS: 240 male Wistar rats were divided randomly into 3 groups. Group SE(n =96) for rats with PTSD-like behavior by constant pulsating current of 100 μA with intratrain frequencies of 16 Hz, pulsating duration of 1 ms, train duration of 10 s and interstimulus interval of 7 min for 5 days with 8 times per day. Group CE(n =96) for control with electrode implanted in hippocampus without stimulation, and Group NC(n =48) for normal control. The activities of Na⁺-K⁺-ATPase and Ca²⁺ -ATPase, levels of intracellular calcium and free calmodulin(CaM), and the total CaM expression were detected in hippocampi of experimental rats. RESULTS: The activities of Na⁺-K⁺-ATPase and Ca²⁺ -ATPase in mitochondria of hippocampal cells in Group SE rats were significantly decreased at 48 h and 72 h after the last stimulation, respectively. The intracellular free calcium levels were increased, and the mean channel fluorescence of intracellular free CaM decreased remarkably at 72 h poststimulation, while the expression of total CaM was significantly elevated at 48 h after the last stimulation in hippocampi of Group SE rats. CONCLUSION: The lasting increased levels of intracellular free calcium and expression of Ca²⁺ -CaM in hippocampus, as well as the dysfunction of Na⁺-K⁺ pump and Ca²⁺ -ATPase in mitochondria may play important roles in the long-term neuropsychological sequelae in PTSD.     

Hypoxia facilitates rapid pacing-induced calcium transient alternations in ventricular myocytes

AIM:To explore the effect of hypoxia on rapid pacing-induced calcium transient alternations in ventricular myocytes.METHODS:Ventricular myocytes were isolated from the heart of adult SD rats and cultured in serum-free hypoxic fluid to set up an in vitro model of hypoxia-induced cardiac injury. The calcium transient and its alternations were investigated under confocal laser scanning microscope. The mitochondrial function was also examined by WST-8 kit. RESULTS:Under normoxic condition, the ventricular myocytes were claviform. Low frequency of pacing, ranging from 60 to 240 min^-1, induced calcium transient, but not calcium transient alternations, which was elicited by the pacing over a threshold frequency of(288 ±27)min^-1. Exposure of the ventricular myocytes to hypoxia did not obviously affect the morphology of the cells, but reduced the threshold frequency of pacing to(227±26) min^-1(P<0.05). Additionally, exposure of the cells to hypoxia repressed the activity of mitochondrial dehydrogenase from(100.2±8.7)%(control group) to(57.6±7.5)%, which was partially blocked by L-type Ca²⁺ channel inhibitor. CONCLUSION:Hypoxia facilitates calcium transient alternations induced by rapid pacing, and the calcium transient alternations are involved in the hypoxia-injured mitochondria function.     

Effect of OX-LDL and simvastatin on PKC activity and cytosolic free Ca2+ in cultured rat aortic smooth muscle cells

AMI:To clarify whether OX-LDL and simvastatin can induce the changes of PKC activity and cytosolic free Ca²⁺ in rat aortic smooth muscle cells (ASMC). METHODS:PKC activity and cytosolic free Ca²⁺ were measured by its ability to transfer phosphate from [³²P]ATP to lysine-rich histone and flow cytometric analysis after loading with the Ca²⁺dye fluo-3/Am, respectively. RESULTS:OX-LDL increased PKC total activity in a dose-dependent manner and induced translocation of PKC from the cytosolic to membrane, while OX-LDL induced biphasic [Ca²⁺]i responses including the rapid initial transient phase and the sustained phase. When simvastatin was added, the translocation of PKC was markedly decreased and simvastatin did not impair the initial peak response to OX-LDL but significantly reduced the subsequent plateau phase. CONCLUSSION:OX-LDL can induce dynamic changes of signal transduction of PKC and cytosolic free Ca²⁺ in ASMC and these two events are closely linked.     

Importance of mitochondrial calcium uniporter in high glucose-induced cardiac myocyte apoptosis

AIM: To investigate the role of mitochondrial calcium uniporter (MCU) in high glucose(HG)-induced apoptosis of cardiac myocytes. METHODS: Cardiac myocytes were exposed to normal glucose (5.5 mmol/L glucose+ 19.5 mmol/L mannitol), HG (25 mmol/L glucose), or HG combined with 5 μmol/L spermine for 72 h. Mitochondrial free Ca²⁺ concentration ([Ca²⁺]_m), MCU at mRNA and protein levels, pyruvate dehydrogenase (PDH) activity, mitochondrial membrane potential (Δψ_m), the levels of ATP and reactive oxygen species (ROS), and apoptosis were determined. RESULTS: The [Ca²⁺]_m, the mRNA and protein levels of MCU, PDH activity, ATP levels, and Δψ_m were reduced (P<0.05), while ROS content and the protein levels of caspase-9 and caspase-3 were increased in HG group (P<0.05). Adding 5 μmol/L spermine returned these parameters toward control levels (P<0.05). Moreover, apoptosis was reduced by adding spermine and HG treatment (P<0.05). CONCLUSION: HG-induced cardiac myocyte apoptosis may be associated with the decreased MCU expression and activity, abnormal mitochondrial Ca²⁺ handling, deviant mitochon-drial respiratory chain, and mitochondrial dysfunction.     

Effects of Shenmai injection on acute myocardial ischemia/reperfusion injury in rats

AIM: To observe the effect of Shenmai injection on the acute myocardial ischemia/ reperfusion injury in rats. METHODS: The left-anterior coronary artery was ligated for 10 minutes and then loosed for 15 minutes to establish the animal model of acute myocardial ischemia/reperfusion injury. During the process, electrocardiogram was traced continuously to observe the arrhythmia caused by reperfusion. The levels of SOD, MDA, Na⁺, K⁺-ATPase and Ca²⁺ -ATPase in ventricular myocardium were measured. The mitochondria was observed through electron microscope. RESULTS: Shenmai injection decreased the incidence of arrhythmia caused by reperfusion and shortened its duration. Shenmai injection improved the activity of SOD, Na⁺, K⁺-ATPase and Ca²⁺ -ATPase, decreased the content of MDA in myocardium and relieved the injury of mitochondria. CONCLUSION: Shenmai injection had a protective effect on acute myocardial ischemia/reperfusion injury in rats. The mechanism may be related to relieving the injury caused by oxygen free radical and calcium overload.