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

用分离的兔窦房结和房室结细胞研究了蛋白激酶C(PKC)对心脏起搏器活动的可能贡献。用膜片钳方法测定膜电流和动作电位。用血管紧张素II、内皮素和佛波酯TPA激活PKC。血管紧张素II和内皮素显著降低窦房结细胞的L钙电流，降低自发放电频率。蛋白激酶A抑制剂或用外源性cAMP透析细胞可抑制这种抑制。经百日咳毒素处理后，血管紧张素II和内皮素的作用也消失。血管紧张素II对I_&lt；Ca&gt；的抑制呈剂量依赖关系，但在较高浓度(大于或等于)30 nM时，先抑制后逐渐增加。蛋白激酶激活剂TPA使心肌细胞内钙离子浓度逐渐升高，幅度约为…更确切地说是15%。这一时间过程类似于高浓度血管紧张素Ⅱ引起的I_t；Ca和Gt；逐渐升高。TPA不能降低血管紧张素II和内皮素的作用。乙酰胆碱也抑制这些起搏细胞的钙和钙。血管紧张素II对乙酰胆碱没有任何额外的作用。根据这些结果，我们认为，蛋白激酶C的激活增强了心肌细胞内钙离子和谷氨酸氨基转移酶，从而产生正性变时性作用。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-腺苷环化酶途径相连。因此，这些血管活性多肽的应用通过降低细胞内cAMP浓度来降低心率。这种负变时性效应可能是通过受体的脱敏和PKC诱导的I&lt；Ca&Gt；的增强而随时间减弱的。PKC对离子通道的长期影响仍有待解决。较少

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