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.     

Physiological function of plasma membrane Ca2+-ATPase isoform 2 in inner ear hair cells of mouse

AIM: To investigate the auditory and balanceable function of hair cell plasma membrane Ca²⁺-ATPase isoform 2 (PMCA2) channel in mouse inner ear.METHODS: Hearing threshold and endocochlear potential (EP) were measured in the PMCA2 homozygous mutants mice,heterozygous mice and wild-type mice by auditory brainstem response (ABR),distortion product otoacoustic emission (DPOAE) and EP recordings,respectively.RESULTS: The auditory function in PMCA2 wild-type mice was normal,the mean value for ABR thresholds in response to click sound stimulus was (13.75±11.08)dB SPL,EP was (91.3±11.0)mV.The mean value for ABR thresholds in response to click sound stimulus was (63.89±12.90)dB SPL in PMCA2 heterozygous mice and significantly increased relative to that observed in PMCA2 wild-type mice (P<0.01).EP in PMCA2 heterozygous mice was about (80.7±9.0) mV and lower than that in PMCA2 wild-type mice but no statistics significance was observed (P>0.05). DPOAE thresholds increased and reduced amplitudes at high frequencies in PMCA2 heterozygous mice compared to wild-type mice.PMCA2 homozygous mutant mice were completely deaf,the ABR wave form was not observed even 100 dB SPL sound stimuli was used,the value of EP was (56.6±13.0) mV lower than that in PMCA2 wild type mice (P<0.05).PMCA2 homozygous mutants mice did not produce DPOAEs,PMCA2 homozygous mutant mice were deaf and demonstrated difficulties in maintaining their balance.CONCLUSION: These data demonstrate that PMCA2 is required for both balance and hearing and suggest that it may be a major Ca²⁺ pump used in endolymph Ca²⁺ maintenance.     

Properties of ACh-sensitive BK channels in mice type Ⅱ vestibular hair cells and its modulation by calcium

AIM: To explore the properties of the acetylcholine (ACh)-sensitive potassium channel in type Ⅱ vestibular hair cells (VHCs Ⅱ) in mice saccular macula and the modulation effect of calcium ions.METHODS: Under the whole-cell patch mode,the pharmacology properties of ACh-sensitive potassium channel and the modulation of calcium ions on ACh-sensitive potassium channel were investigated.RESULTS: Following extracellular perfusion of ACh,VHCs Ⅱ displayed a slow and sustained outward current,which was sensitive to tetraethylammonium (TEA,5 mmol/L) and charybdotoxin (CTX,100 nmol/L),but not sensitive to 4-aminopyride (4-AP,15 μmol/L).ACh-sensitive potassium current was inhibited by intracellular application of ethylene glycol-bis (B-aminoethylether)-N,N,N,N-tetraacetic- acid (EGTA,5 mmol/L) and extracellular perfusion of Cd2+ and Ni2+,respectively.Intracellular application of heparin (8 g/L) failed to inhibit ACh-sensitive potassium current.CONCLUSION: Extracellular application of ACh activates the big conductance,calcium-dependent potassium current (BK) in VHCs Ⅱ of mice,which is potently modulated by extracellular Ca2+ ions.However,intracellular IP3-dependent Ca2+ ions release mechanism is not involved in the activation of the ACh-sensitive BK channel.     

Effect of diazoxide on change of H2O2 in rat pulmonary artery smooth muscle cells and proliferation of hypoxic rat pulmonary artery smooth muscle cells

AIM: To investigate the contribution of diazoxide,an opener of mitochondrial ATP-sensitive K+ channel (MitoK_ATP),and mitochondrial membrane potential (ΔΨm) to change of H₂O₂ in rat pulmonary artery smooth muscle cells (PASMCs) and to unbalance between cell proliferation and apoptosis of PASMCs induced by hypoxia.METHODS: The rat PASMCs were isolated from fresh normal lung tissues and cultured,which were divided into 6 groups,as follows: ① control group;② diazoxide group;③ 5-HD group;④chronic hypoxia group;⑤ chronic hypoxia+diazoxide group;⑥ chronic hypoxia +5-HD group.The relative change in mitochondrial potential was detected with rhodamine fluorescence (R-123) technique.The level of H₂O₂ in rat PASMCs was detected with chemiluminescence method.The proliferation of rat PASMCs was examined by cell cycle analysis and MTT colorimetric assay.RESULTS: After exposed to diazoxide for 24 h,the intensity of R-123 fluorescence,the level of H₂O₂ and the A value in normoxic rat PASMCs were significantly increased,and the apoptosis of rat PASMCs was significantly decreased as compared with control group (P<0.05).However,there were no significant changes in these tests after the rat PASMCs had been exposed to 5-HD for 24 h.Chronic hypoxia or chronic hypoxia+diazoxide markedly increased the intensity of R-123 fluorescence,the level of H₂O₂ and the A value in rat PASMCs,and also markedly decreased the apoptosis of rat PASMCs as compared with control group (P<0.05),and these changes were more significant in chronic hypoxia +diazoxide group than those in chronic hypoxia group (P<0.05).5-HD partly weakened the effect of hypoxia on the intensity of R-123 fluorescence,the level of H₂O₂,the A value and the apoptosis of rat PASMCs (P<0.05).Significant and positive correlations were found between the intracellular H₂O₂ and the R-123 fluorescence or the A value.Significant and negative correlation was found between the intracellular H₂O₂ and the apoptosis of rat PASMCs.CONCLUSION: The results suggest that the opening of MitoK_ATP followed by a depolarization of ΔΨm can contribute to the increase in the level of H₂O₂ in rat PASMCs and to the proliferation of rat PASMCs induced by hypoxia.This might be a mechanism of the development of hypoxic pulmonary hypertension.     

Pacific-Ciguatoxin-2 and Brevetoxin-1 Induce the Sensitization of Sensory Receptors Mediating Pain and Pruritus in Sensory Neurons

Ciguatera fish poisoning (CFP) and neurotoxic shellfish poisoning syndromes are induced by the consumption of seafood contaminated by ciguatoxins and brevetoxins. Both toxins cause sensory symptoms such as paresthesia, cold dysesthesia and painful disorders. An intense pruritus, which may become chronic, occurs also in CFP. No curative treatment is available and the pathophysiology is not fully elucidated. Here we conducted single-cell calcium video-imaging experiments in sensory neurons from newborn rats to study in vitro the ability of Pacific-ciguatoxin-2 (P-CTX-2) and brevetoxin-1 (PbTx-1) to sensitize receptors and ion channels, (i.e., to increase the percentage of responding cells and/or the response amplitude to their pharmacological agonists). In addition, we studied the neurotrophin release in sensory neurons co-cultured with keratinocytes after exposure to P-CTX-2. Our results show that P-CTX-2 induced the sensitization of TRPA1, TRPV4, PAR2, MrgprC, MrgprA and TTX-r NaV channels in sensory neurons. P-CTX-2 increased the release of nerve growth factor and brain-derived neurotrophic factor in the co-culture supernatant, suggesting that those neurotrophins could contribute to the sensitization of the aforementioned receptors and channels. Our results suggest the potential role of sensitization of sensory receptors/ion channels in the induction or persistence of sensory disturbances in CFP syndrome.     

北京居民花卉消费特征分析

以问卷调查数据为基础,运用SPSS软件分析了北京市城市居民花卉消费行为的基本特征。研究结果表明,居民花卉消费总体需求旺盛,居民花卉消费个体需求多样化,消费者的花卉购买方式以实体市场为主,花卉消费时段集中、节日特征明显,花卉消费从众心理明显,消费预期较为乐观但不确定性较强。进而探讨了不同细分市场的花卉消费特征,并据此提出了促进花卉消费的营销建议。     

电子商务对我国农村地区饲料营销的影响

随着社会经济的不断发展、互联网技术的不断成熟,虚拟化、快捷化电子商务模式的出现彻底改变了局限于特定时间和空间的传统经营模式,丰富了企业的营销方式。农村地区是我国畜牧业和养殖业发展的重点区域,饲料需求较强,如何通过电子商务积极创新营销策略增加收益,事关饲料企业的发展。本文通过阐述我国农村地区饲料营销的电子商务发展现状,进而分析电子商务对我国农村地区饲料营销的有利和不利影响,以期对饲料企业未来电子商务的发展方向进行展望。     

论绿色营销对企业发展的重要性

中国已加入世贸，我国企业要在新世纪的竞争中取胜，必须实行绿色营销。对绿色营销的含义，实施绿色营销的背景、重要性以及措施进行了探讨。     

高职农产品营销课程目标导向学习法应用研究

高职农产品营销课程的教学要在抓住其自身教学特点的同时找准存在的问题.在运用目标导向理论与建构主义理论的基础上进行农产品市场营销课程教学法的创新,打造"510模式".在以学生为中心的基础上,通过理论与实践的自主学习锻炼,再通过教师和同学集体的反馈以及教师最后的总结,可以使学生更好地掌握所学知识,提升营销能力.通过教法实践,在取得了较好效果的同时,也出现了学生自学阶段效果差、独自实践与小组要求有差距、组内协调互帮效果不好等问题.应该在强调学生为中心的同时,适当加强教师的引导作用,做到学生主体性与教师主导性的有机统一.