Boachie-Ansah G, Kane K A, Parratt J R
Department of Physiology and Pharmacology, University of Strathclyde, Glasgow, Scotland, U.K.
J Cardiovasc Pharmacol. 1989 Feb;13(2):291-8. doi: 10.1097/00005344-198902000-00018.
The aim of this study was to examine the electrophysiological effects of isoprenaline, phenylephrine, and noradrenaline on sheep Purkinje fibers in vitro, superfused either with a normal or with a modified physiological salt solution (PSS) designed to mimic some of the conditions occurring during mild myocardial ischemia (hyperkalemia, hypoxia, and acidosis). Intracellular microelectrode recording techniques were used to record resting and action potentials. Noradrenaline (10(-7) to 10(-5) M) and phenylephrine (10(-7) to 10(-5) M) prolonged the action potential of normal fibers in a concentration-dependent manner, the effect of phenylephrine being greater than that of noradrenaline. The only effect of isoprenaline (10(-7) to 10(-5) M) was a slight hyperpolarization. The modified PSS caused marked reductions in resting membrane potential, upstroke, and duration of the action potential. On these depressed fibers isoprenaline, noradrenaline, and phenylephrine all prolonged the action potential, and in the case of noradrenaline the duration of the abbreviated action potential was restored beyond control. This effect of noradrenaline and isoprenaline was more marked under ischemic than normal conditions, whereas the opposite was true of phenylephrine. In the presence of effective alpha- or beta-adrenoceptor blockade, the noradrenaline-induced prolongation of the "ischemia"-abbreviated action potential was attenuated. In some of the preparations exposed to simulated ischemia, noradrenaline caused inexcitability. In conclusion, isoprenaline, phenylephrine, and noradrenaline exhibited different electrophysiological effects on mildly "ischemic" sheep Purkinje fibers compared to their effects on normal fibers.
本研究的目的是在体外研究异丙肾上腺素、去氧肾上腺素和去甲肾上腺素对绵羊浦肯野纤维的电生理作用，这些纤维用正常或改良的生理盐溶液（PSS）进行灌流，改良的PSS旨在模拟轻度心肌缺血（高钾血症、缺氧和酸中毒）期间出现的一些情况。采用细胞内微电极记录技术记录静息电位和动作电位。去甲肾上腺素（10⁻⁷至10⁻⁵M）和去氧肾上腺素（10⁻⁷至10⁻⁵M）以浓度依赖的方式延长正常纤维的动作电位，去氧肾上腺素的作用大于去甲肾上腺素。异丙肾上腺素（10⁻⁷至10⁻⁵M）的唯一作用是轻微超极化。改良的PSS导致静息膜电位、动作电位的上升支和持续时间显著降低。在这些受抑制的纤维上，异丙肾上腺素、去甲肾上腺素和去氧肾上腺素均延长了动作电位，就去甲肾上腺素而言，缩短的动作电位持续时间恢复到对照水平以上。去甲肾上腺素和异丙肾上腺素的这种作用在缺血条件下比正常条件下更明显，而去氧肾上腺素则相反。在有效的α或β肾上腺素能受体阻断存在的情况下，去甲肾上腺素诱导的“缺血”缩短动作电位的延长减弱。在一些暴露于模拟缺血的制剂中，去甲肾上腺素导致兴奋性丧失。总之，与它们对正常纤维的作用相比，异丙肾上腺素、去氧肾上腺素和去甲肾上腺素对轻度“缺血”的绵羊浦肯野纤维表现出不同的电生理作用。
