Effects of adenosine receptor stimulation on guinea pig cardiac myocytes

已知内源性腺苷可以调节心肌细胞的生理功能，并在缺血和再灌流过程中发挥保护作用。为了探讨腺苷类似物作为心肌治疗药物的有效性，我们首先在全细胞膜片钳结构中检测了腺苷对豚鼠心肌细胞的电生理效应。腺苷使心房肌细胞动作电位时程缩短，并使静息膜电位超极化，但对心肌细胞膜电位无明显影响。当心房细胞与百日咳毒素(LAP)预先孵育时，腺苷不能缩短时程，证实了腺苷受体的存在。与IAP敏感的GTP结合蛋白偶联。在L型钙离子通道阻断剂尼卡地平的存在下，腺苷使0 mV的外向膜电流增加，这表明腺苷引起了特定的K~(+)-外向电流。腺苷A_1受体激动剂N^6-环己基腺苷(CHA)，而不是A_2或A_3受体激动剂Rep…此外，腺苷对动作电位时程的缩短作用和对心房肌细胞外向膜电流的增加作用均明显增强。这些作用可被A_1受体拮抗剂8-环戊基-1，3-二丙基黄嘌呤(DPCPX)完全阻断。KATP通道阻断剂格列本脲可完全消除CHA对APR的缩短效应，并部分消除其对膜外向电流的影响，提示CHA的作用是通过激活质膜上的K_1、ATP和Gt_1通道实现的。此外，ChA效应对细胞外向膜电流的影响可通过蛋白激酶C抑制剂白屈菜红碱预先孵育而完全消除，并可被线粒体K；lt；ATP&gt；通道的特异性抑制剂5-羟基癸酸(5-HD)部分抑制。这些结果提示，腺苷A_1受体刺激引起的时程缩短，部分是通过蛋白激酶C和5-HD敏感的细胞内信号通路激活K&lt；ATP&Gt；通道，这可能参与了腺苷在缺血和再灌流过程中发挥保护作用的机制。较少

Endogenous adenosine is known to regulate the physiological cardiomyocyte function and to exert a protective action during ischemia and reperfusion. To explore the usefulness of adenosine analogue as a myocardial therapeutic agent, we first examined the electrophysiological effects of adenosine on guinea pig cardiomyocytes in the whole cell patch-clamp configuration. Adenosine shortened the action potential duration (APD) and hyperpolarized the resting membrane potential of atrial but not ventricular myocytes. When atrial cells were preincubated with pertussis toxin (LAP), adenosine did not shorten the APD, confirming that adenosine receptors. couple to the IAP-sensitive GTP-binding protein. Adenosine increased the outward membrane current at 0mV in the presence of nicardipine, an L-type Ca^<2+> channel blocker, which suggests that adenosine elicited the specific K^+-outward current. Adenosine A_1 receptor agonist, N^6-cyclohexyladenosine (CHA), but not A_2 or A_3 receptor agonist, rep … More roduced both the adenosine-induced shortening effect on APD and the increasing effect on the outward membrane current of atrial myocytes. These effects were completely abolished by A_1 receptor antagonist, 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX). Glybenclamide, a KATP channel blocker, completely abolished the CHA-induced shortening effect on APR and also partially abolished the effect on the outward membrane current, which suggests that the effects of CHA are mediated by the activation of K_<ATP> channels on the plasma membrane. Further, the effect of CHA effect, on the outward membrane current was completely abolished by preincubating the cells with chelerythrine, a protein kinase C inhibitor, and was partially,inhibited by 5-hydroxydecanoic acid (5-HD), known as a specific inhibitor of mitochondrial K_<ATP> channels. These results suggest that the shortening of APD caused by adenosine A_1 receptor stimulation was conducted in part through an activation of K_<ATP> channels via protein kinase C and 5-HD-sensitive intracellular signaling pathways, which may be involved in the mechanisms by which adenosine exerts a protective action during ischemia and reperfusion. Less