去甲肾上腺素、乙酰胆碱对绵羊心肌浦肯野纤维瞬时性内向离子流的影响

EFFECTS OF NORADRENALINE AND ACETYLCHOLINE ON TRANSIENT INWARD CURRENT IN SHEEP CARDIAC PURKINJE FIBERS

用电压箝制术观察了去甲肾上腺素、乙酰胆碱对绵羊浦肯野纤维由乙酰毒毛旋花子甙元诱发的瞬时性内向离子流(I_Ti)的效应。当乙酰毒毛旋花子甙元浓度为4.5×10^(-8)mol/L 时,诱发出的I_(T1)稳定并能维持约1.5h。去甲肾上腺素1.5×10^(-6)mol/L,可使I_(Ti)的峰值由11.4±2.5nA 增加到14.5±4.1nA(n=11,P<O.01),I_(Ti)的时程由688±278ms 缩短到556±237 ms(n=11,P<0.05)。乙酰胆碱2.5×10^(-6)mol/L 可使I_(Ti)峰值降低,由对照的13.4±3.8nA 减至10.6±3.2nA (n=8,P<0.01),并使 I_(Ti)时程由653±193ms 延长到741±222ms(n=8,P<0.05)。在去甲肾上腺素2×10_(-6)mol/L 作用基础上,乙酰胆碱2.5×10_(-6)mol/L 可使 I_(Ti)幅值由14.8±7.7减小到10.0±6.7 nA(n=6,P<0.01)。本工作也对去甲肾上腺素的作用途径进行了探讨,当用 Mn^(2+)0.75mmol/L 阻断 I_(si)后,再用去甲肾上腺素2×10^(-6)mol/L 灌流标本,I_(Si)幅值无明显变化,而 I_(Ti)幅值由2.2±0.2nA 增加到4.9±1.1 nA(n=6,P<0.01),表明去甲肾上腺素增加 I_(Ti)的作用并不完全依赖于其对 I_(si)的增值效应。

By using two-microelectrode voltage clamp technique,the effect of noradre-naline and acetylcholine on transient inward current(I_(Ti)induced by acetyl-strophanthidin was observed in sheep cardiac Purkinje fibers.In the presenceof acetyl strophanthidin(4.5×10_(-8)mol/L),the stability of I_(Ti)could be main-tained for about 1.5 h.Noradrenaline(1.5×10^(-6)mol/L)increased the I_(Ti)from 11.4±2.5 nA to 14.5±4.1 nA(n=11,P<0.01)and shortened the I_(Ti)duration from 688±278 ms to 556±237 ms(n=11,P<0.05).Acetylcholine(2.5×10^(-6)mol/L)decreased the I_(Ti)amplitude from 13.4±3.8 nA to 10.6±3.2 nA(n=8,P<0.01)and prolonged the I_(Ti)duration from 653±193 ms to741±222 ms(n=8,P<0.05).Acetylcholine(2.5×l0^(-6) mol/L)also decrea-sed the I_(Ti)amplitude in the preparation pretreated with noradrenaline(2×10^(-6)mol/L)from 14.8±7.7 nA to 10.0±6.7 nA(n=6,P<0.01).In addition,themechanism of noradrenaline effect was also studied.When the slow inward cur-rent(Isi)was blocked by Mn^(2+)(0.75 mmol/L),noradrenaline still increasedthe I_(Ti)amplitude from 2.2±0.2 nA to 4.9±1.1 nA(n=6,P<0.01)but hadno effect on Isi,suggesting that noradrenaline has a direct effect on I_(Ti),