Protein kinase C-mediated regulation of the electrical activity in cardiac pacemaker cells (1995)

用兔窦房结细胞和房室结细胞研究了蛋白激酶C （PKC）对心脏起搏器活性的可能贡献。膜片钳法测定膜电流和动作电位。为了激活PKC，血管紧张素II、内皮素和一种磷脂酯TPA被激活。血管紧张素和内皮素显著降低窦房结细胞l型Ca电流I_<Ca>，降低自燃率。这种对I_<Ca>的抑制作用被蛋白激酶a抑制剂或外源性cAMP细胞透析所抑制。百日咳毒素预处理也可消除血管紧张素II和内皮素的作用。血管紧张素ii诱导的I_<Ca>的抑制呈剂量依赖性，但在较高浓度（大于或等于30 nM）下，I_<Ca>在初始抑制后逐渐升高。TPA是一种蛋白激酶激活剂，可使I_<Ca>逐渐升高约15%。这个时间过程类似于高浓度血管紧张素II所观察到的I_< ca>的逐渐增加。TPA预处理并没有降低血管紧张素II和内皮素的作用。乙酰胆碱还能抑制这些起搏细胞中的I_<Ca>，而血管紧张素II对乙酰胆碱没有任何额外的作用。综上所述，蛋白激酶C的激活可增强I_<Ca>，从而产生正向变时效应。然而，与磷脂酶c蛋白激酶途径偶联的受体也与百日咳毒素敏感的g_i -腺苷酸环化酶途径相连。因此，这些血管活性肽的应用通过降低细胞内cAMP浓度来降低心率。这种负变时效应随着时间的推移而减弱，可能是通过受体的脱敏和pkc诱导的I_<Ca>的增强。PKC对离子通道的长期影响仍有待解决。少

Possible contribution of protein kinase C (PKC) to the cardiac pacemaker activity was investigated using sinoatrial and atrioventricular node cells isolated from rabbits. The membrane currents and action potentials were measured with the patch clamp method. In order to activate the PKC, angiotensin II, endothelin and a phorbol ester TPA were tised. Angiotensin II and endothelin significantly reduced the L-type Ca current I_<Ca> in sinoatrial node cells, and reduced the spontaneous firing rate. This inhibition of the I_<Ca> was inhibited by a protein kinase A inhibitor or dialysis of the cells with extrinsic cAMP. A pretreatment with pertussis toxin also abolished the effects of angiotensin II and endothelin. The angiotensin II-induced inhibition of I_<Ca> was dose-dependent, however at higher concentrations (【greater than or equal】30 nM), the initial inhibition was followed by a graduai increase in the I_<Ca>. TPA, a protein kinase activator, gradually increased the I_<Ca> by approxima … More tely 15%. This time course resembled the gradual increase in I_<Ca> observed with high concentrations of angiotensin II. The pretreatment with TPA did not reduce the effects of angiotensin II and endothelin. Acetylcholine also inhibited the I_<Ca> in these pacemaking cells, and angiotensin II did not show any additional effect to acetylcholine. According to these results, it is concluded that activation of protein kinase C enhances I_<Ca>, which can cause a positive chronotropic effect. However, the receptors which are coupled with the phospholipase C-protein kinase pathway are also linked with the pertussis toxin-sensitive G_i-adenylate cyclase pathway. Thus, application of these vasoactive peptides reduces the heart rate by lowering the intracellular cAMP concentration. This negative chronotropic effect is attenuated with time presumably through the desensitization of the receptor and PKC-induced potentiation of I_<Ca>. Long-term effects of PKC on the ion channels remain to be resolved. Less