Jiang C, Mochizuki S, Poole-Wilson P A, Harding S E, MacLeod K T
Department of Cardiac Medicine, National Heart and Lung Institute, London, United Kingdom.
Cardiovasc Res. 1994 Jun;28(6):851-7. doi: 10.1093/cvr/28.6.851.
The aim was to investigate the effects of lemakalim on action potential duration, intracellular free calcium ([free Ca2+]i), and cell contraction in human and guinea pig cardiac myocytes. In addition, the possible modulation by pH of lemakalim induced activation of ATP sensitive potassium (KATP) channels was assessed.
Single ventricular myocytes were enzymatically dissociated from adult male guinea pigs (300-600 g). Single myocytes were isolated from human ventricular tissues. Cells were loaded with the acetoxymethyl ester form of fura-2 to monitor changes in [free Ca2+]i and subjected to conventional electrophysiological techniques.
In guinea pig cells, lemakalim (3, 10, 30 microM) reduced action potential duration in a concentration dependent manner. This decrease was accompanied by hyperpolarisation of the resting membrane potential. Lemakalim (3, 10, 30 microM) reduced the systolic fura-2 fluorescence ratio without having a significant effect on diastolic fluorescence and also reduced the cell contraction in concentration dependent manner. Glibenclamide (1 microM), a specific inhibitor of KATP channels, did not affect action potential duration, fura-2 fluorescence ratio, or cell contraction in the absence of lemakalim. However, the same dose of glibenclamide markedly inhibited the lemakalim induced decrease in action potential duration, fura-2 fluorescence ratio, and cell contraction. Reducing extracellular pH enhanced the decrease in action potential duration induced by lemakalim. In human ventricular myocytes, lemakalim (3, 10 and 30 microM) caused a decrease in action potential duration and systolic fura-2 fluorescence ratio. The reduction in action potential duration and fura-2 fluorescence ratio was also reversed by glibenclamide (1 microM).
These results suggest that lemakalim reduces systolic [free Ca2+]i by activating ATP sensitive potassium channels which results in a decrease of action potential duration in guinea pig and human ventricular myocytes. The reduction in [free Ca2+]i mediates the negative inotropic effect induced by lemakalim. In addition, pH may modulate the KATP channel activation by the channel opener.
研究雷马卡林对人和豚鼠心肌细胞动作电位时程、细胞内游离钙（[游离Ca2+]i）及细胞收缩的影响。此外，评估pH对雷马卡林诱导的ATP敏感性钾（KATP）通道激活的可能调节作用。
从成年雄性豚鼠（300 - 600 g）中酶解分离单个心室肌细胞。从人心脏心室组织中分离单个心肌细胞。用乙酰氧甲酯形式的fura - 2加载细胞以监测[游离Ca2+]i的变化，并采用传统电生理技术。
在豚鼠细胞中，雷马卡林（3、10、30 μM）以浓度依赖性方式缩短动作电位时程。这种缩短伴随着静息膜电位的超极化。雷马卡林（3、10、30 μM）降低收缩期fura - 2荧光比率，而对舒张期荧光无显著影响，并且也以浓度依赖性方式减少细胞收缩。格列本脲（1 μM），一种KATP通道的特异性抑制剂，在无雷马卡林时不影响动作电位时程、fura - 2荧光比率或细胞收缩。然而，相同剂量的格列本脲显著抑制雷马卡林诱导的动作电位时程缩短、fura - 2荧光比率降低及细胞收缩。降低细胞外pH增强了雷马卡林诱导的动作电位时程缩短。在人心室肌细胞中，雷马卡林（3、10和30 μM）导致动作电位时程和收缩期fura - 2荧光比率降低。格列本脲（1 μM）也使动作电位时程和fura - 2荧光比率的降低逆转。
这些结果表明，雷马卡林通过激活ATP敏感性钾通道降低收缩期[游离Ca2+]i，这导致豚鼠和人心室肌细胞动作电位时程缩短。[游离Ca2+]i的降低介导了雷马卡林诱导的负性肌力作用。此外，pH可能调节通道开放剂对KATP通道的激活。
