The effect of acetylcholine (ACh) on the membrane current components in guinea-pig papillary muscle was studied by the single sucrose gap voltage clamp method. 2. The slow inward current (is) elicited by various depolarizations from the holding potential of -40 mV was evidently diminished by ACh greater than 5 x 10(-7) M. The amplitude of is, estimated as the difference between the peak of is and the current at 150 msec, was reduced to 56.8 +/- 12.9% (mean +/- S.D., n = 34) by 2 x 10(-8) M-ACh when estimated at the membrane potential where the amplitude was maximal. 3. is was suppressed almost completely by 2 mM-Co2+, is obtained by subtracting the current remaining in 2 mM-Co2+ was also diminished to the same extent by 2 x 10(-6) M-Ach with little change in its time course; the degree of decrease was not dependent on the membrane potential. 4. The time-dependent outward current during the depolarizing pulse was also diminished by 2 x 10(-6) M-Ach. Correspondingly, the positive tail current obtained when the membrane was repolarized to the holding potential of -40 mV after various 1 sec depolarizations was reduced in a proportionate manner to 68.6 +/- 7.3% (n = 10). 5. The time-independent inward rectifying outward current was not affected by 2 x 10(-6) M-Ach. 6. Atropine (10(-6) M) restored is and the time-dependent outward current which had been previously depressed by 2 x 10(-6) M-ACh. 7. ACh may decrease tension development by depressing is, thereby preserving the duration of the action potential with relatively little change, since, different from atrial muscle, ACh does not increase the outward current in mammalian ventricular muscle.
摘要
采用单蔗糖间隙电压钳法研究了乙酰胆碱（ACh）对豚鼠乳头肌膜电流成分的影响。2. 从 -40 mV 的钳制电位进行各种去极化所引发的慢内向电流（is），在 ACh 浓度大于 5×10⁻⁷ M 时明显减小。当在 is 幅度最大的膜电位处进行估算时，2×10⁻⁸ M - ACh 可使 is 的幅度（估算为 is 峰值与 150 毫秒时电流的差值）降至 56.8±12.9%（平均值±标准差，n = 34）。3. 2 mM - Co²⁺几乎完全抑制 is，通过减去 2 mM - Co²⁺中剩余电流得到的 is，也会被 2×10⁻⁶ M - Ach 以相同程度减小，其时程变化不大；减小程度与膜电位无关。4. 去极化脉冲期间的时间依赖性外向电流也会被 2×10⁻⁶ M - Ach 减小。相应地，在进行各种 1 秒去极化后，当膜复极化至 -40 mV 的钳制电位时所获得的正向尾电流会以相应比例降至 68.6±7.3%（n = 10）。5. 时间非依赖性内向整流外向电流不受 2×10⁻⁶ M - Ach 的影响。6. 阿托品（10⁻⁶ M）可恢复先前被 2×10⁻⁶ M - ACh 抑制的 is 和时间依赖性外向电流。7. ACh 可能通过抑制 is 来降低张力发展，从而在相对较小变化的情况下维持动作电位的持续时间，因为与心房肌不同，ACh 在哺乳动物心室肌中不会增加外向电流。
