心肌d_1-肾上腺素受体激动对豚鼠心室乳头肌的影响

EFFECT OF MYOCARDIAL α_1-ADRENOCEPTOR STIMULATION ON THE GUINEA-PIG VENTRICULAR PAPILLARY MUSCLE

用α-受体激动剂新福林(5.0×10^(-6)mol/L)激动豚鼠心室乳头肌α-受体,观察乳头肌跨膜动作电位和收缩力的变化,并用α_1-受体阻断剂哌唑嗪(5.0×10^(-7)mol/L)和α_2-受体阻断剂育亨宾(5.0×10^(-7)mol/L)来判别何种α-受体亚型参与。实验中,β-受体阻断剂心得安(1.0×10^(-6)mol/L)始终存在。实验结果表明心肌α_1-受体激动使(1) 豚鼠心室乳头肌收缩力增强;(2) 收缩峰时间延长;舒张期不变;(3) 快反应动作电位时程延长;(4) 慢反应动作电位零相最大除极速率增加。提示,心肌α_1-受体激动的电生理和正性变力效应的离子机制可能是促进慢内向离子流,使Ca^(2+)内流增加。

The α-adrenoceptor agonist phenylephrine (5.0×10^(-6) mol/L )was used to stimulate myocardial α-adrenoceptors of the guinea-pig ventricular papillary muscle, and changes of transmembrane action potential and contractile force of the muscle were observed. The α_1-adrenoceptor blocker prazosin (5.0×10^(-7) mol/L) and the α_2-adrenoceptor blocker yohimbine (5.0×10^(-7) mol/L)were used to determine which subtype of α-adrenoceptor is responsible for the effects. The β-adrenoceptor blocker propranolol (1.0×10^(-6) mol/L) was used throughout the experiment. The results show that the myocardial α_1-adrenoceptor stimulation (1) increases the contractile force of the guinea-pig ventricular papillary muscle, (2) prolongs the time to peak contractile force while the duration of relaxation is not altered, (3) prolongs the fast response action potential duration, and (4) increases the maximal rate of depolarization during the phase 0 of the slow response action potential. It is suggested that the electrophysiological and positive inotropie effects of myocardial α_1-adrenoceptor stimulation might be due to the activation of the slow inward current and an increase in Ca^(2+) influx.