Irisawa H, Kokubun S
J Physiol. 1983 May;338:321-37. doi: 10.1113/jphysiol.1983.sp014675.
Effects of ATP and of cyclic AMP on membrane current systems were investigated in isolated single ventricular cells from guinea-pig hearts by applying the suction electrode method. The intracellular milieu was dialysed with various solutions which were perfused continuously through the suction pipette. The presence of ATP, cyclic AMP and EGTA in the perfusion solution kept the plateau phase of the action potential almost intact for as long as 30 min. With depolarizing voltage-clamp pulses from holding potentials between -30 and -40 mV, the slow inward current (isi) was activated at potentials positive to -20 mV. The inactivation time course of isi was fitted by two exponential components in the potential range between -10 mV and +30 mV. By increasing ATP from 2 to 9.5 mM in the solution, the amplitude of isi was increased and the slow component of inactivation was accelerated. The steady-state current-voltage relationship (I-V curve), exhibited a negative slope that became steeper after increasing the ATP concentration. The current was shifted towards the outward direction between -40 mV and -10 mV and became more inward between -10 mV and +40 mV. Increase of the cyclic AMP concentration from 30 to 60 microM also enhanced the amplitude of isi, but the negative slope in the steady-state I-V curve was unaffected. Assuming that the concentration of free Ca2+ in the cell was well buffered at a low level by the EGTA-Ca buffer solution in the pipette, it was concluded that [ATP]i and [cyclic AMP]i exert a direct influence on membrane current systems of the ventricular cell.
采用吸力电极法，研究了ATP和环磷酸腺苷（cAMP）对豚鼠心脏分离的单个心室细胞中膜电流系统的影响。通过吸力移液器连续灌注各种溶液，对细胞内环境进行透析。灌注液中ATP、cAMP和乙二醇双四乙酸（EGTA）的存在可使动作电位的平台期在长达30分钟内几乎保持完整。当从-30至-40 mV的钳制电位施加去极化电压钳脉冲时，在正于-20 mV的电位下激活慢内向电流（isi）。在-10 mV至+30 mV的电位范围内，isi的失活时间过程由两个指数成分拟合。通过将溶液中ATP的浓度从2 mM增加到9.5 mM，isi的幅度增加，失活的慢成分加速。稳态电流-电压关系（I-V曲线）呈现负斜率，在增加ATP浓度后变得更陡。电流在-40 mV至-10 mV之间向外偏移，在-10 mV至+40 mV之间向内偏移更多。将cAMP浓度从30 μM增加到60 μM也增强了isi的幅度，但稳态I-V曲线中的负斜率未受影响。假设移液器中的EGTA-Ca缓冲溶液将细胞内游离Ca2+的浓度很好地缓冲在低水平，得出结论：细胞内ATP（[ATP]i）和细胞内环磷酸腺苷（[cAMP]i）对心室细胞的膜电流系统有直接影响。
