Ebihara L, Mathias R T
Biophys J. 1985 Sep;48(3):449-60. doi: 10.1016/S0006-3495(85)83800-5.
Plateau and pacemaker currents from tissue cultured clusters of embryonic chick heart cells were studied in the time domain, using voltage-clamp steps, and in the frequency domain, using a wide-band noise input superimposed on a steady holding voltage. In the presence of tetrodotoxin to block the sodium channel, a depolarizing voltage step into the plateau range elicited: (a) a rapid (approximately equal to 2 ms) activation of the slow inward current; (b) a subsequent slower (approximately equal to 25 ms) decline in the slow inward current; and (c) activation of a very slow (5 to 10 s) outward current. Impedance studies in this voltage range could clearly resolve two voltage-dependent processes, which appeared to correspond to points b and c above because of their voltage dependence, pharmacology, and time constants. A correlate of point a was also probably present but difficult to resolve owing to the fast time constant of activation for the slow inward channel. At voltages negative to -50 mV a new voltage-dependent process could be resolved, which, because of its voltage dependence and time constant, appeared to represent the pacemaker channel (also termed If or IK2). In the Appendix, linear models of voltage-dependent channels and ion accumulation/depletion are derived and these are compared with our data. Most of the above-mentioned processes could be attributed to voltage-dependent channels with kinetics similar to those observed in time domain, voltage-clamp studies. However, the frequency domain correlate of the decline of the slow inward current was incompatible with channel gating, rather, it appears accumulation/depletion of calcium may dominate the decline in this preparation.
利用电压钳位步骤在时域中，以及在稳定的保持电压上叠加宽带噪声输入在频域中，研究了来自胚胎鸡心脏细胞组织培养簇的平台电流和起搏电流。在存在河豚毒素以阻断钠通道的情况下，向平台范围的去极化电压阶跃引发了：(a) 缓慢内向电流的快速（约2毫秒）激活；(b) 随后缓慢内向电流的较慢（约25毫秒）下降；以及(c) 非常缓慢（5至10秒）外向电流的激活。在该电压范围内的阻抗研究可以清楚地分辨出两个电压依赖性过程，由于它们的电压依赖性、药理学和时间常数，这两个过程似乎分别对应于上述的b点和c点。a点的相关过程可能也存在，但由于缓慢内向通道激活的快速时间常数而难以分辨。在电压低于-50 mV时，可以分辨出一个新的电压依赖性过程，由于其电压依赖性和时间常数，它似乎代表起搏通道（也称为If或IK2）。在附录中，推导了电压依赖性通道和离子积累/消耗的线性模型，并将其与我们的数据进行了比较。上述大多数过程可归因于动力学与在时域电压钳研究中观察到的类似的电压依赖性通道。然而，缓慢内向电流下降的频域相关过程与通道门控不相符，相反，在这种制剂中，钙的积累/消耗似乎主导了下降过程。
