Satoh H, Sperelakis N
Department of Physiology and Biophysics, University of Cincinnati, College of Medicine, Ohio 45267-0576.
J Dev Physiol. 1991 Apr;15(4):247-52.
Whole-cell voltage-clamp experiments were performed to examine the underlying currents flowing during the pacemaker potential of spontaneously-beating embryonic chick ventricles. The holding potential was -30 mV. Long-duration (3 s) hyperpolarizing pulses were applied to -40 to -120 mV, in increments of 10 mV. A marked hyperpolarization-activated inward current (If) was produced. In cells from 3-day-old hearts, the threshold potential for the inward current was -50 to -60 mV. In 17-day-old cells, there was almost no If current. At -120 mV, the inward current was -93.8 +/- 6.3 pA (n = 5) in 3-day-old cells and -15.7 +/- 2.8 pA (n = 5) in 17-day-old cells. The average capacitances were 10.1 +/- 2.0 pF (n = 17) in 3-day-old cells, and 6.9 +/- 1.2 pF (n = 14) in 17-day-old cells. The reduction of If paralleled the decrease in spontaneous activity. In the presence of 3 mM CsCl, the inward current was blocked completely, and the tail current was reduced. In addition, 3 mM CsCl depressed the spontaneous action potentials and had a negative chronotropic effect. These results indicate that the hyperpolarization-activated inward If current exists in young embryonic chick heart cells, and decreases during development. This If current may contribute somewhat to the electrogenesis of the pacemaker potential.
进行全细胞电压钳实验以检测自发搏动的胚胎鸡心室起搏电位期间流动的基础电流。钳制电位为-30 mV。施加持续时间较长（3 s）的超极化脉冲至-40至-120 mV，增量为10 mV。产生了明显的超极化激活内向电流（If）。在3日龄心脏的细胞中，内向电流的阈值电位为-50至-60 mV。在17日龄的细胞中，几乎没有If电流。在-120 mV时，3日龄细胞的内向电流为-93.8±6.3 pA（n = 5），17日龄细胞的内向电流为-15.7±2.8 pA（n = 5）。3日龄细胞的平均电容为10.1±2.0 pF（n = 17），17日龄细胞的平均电容为6.9±1.2 pF（n = 14）。If电流的减少与自发活动的降低平行。在存在3 mM CsCl的情况下，内向电流被完全阻断，尾电流减少。此外，3 mM CsCl抑制自发动作电位并具有负性变时作用。这些结果表明，超极化激活内向If电流存在于幼龄胚胎鸡心脏细胞中，并在发育过程中减少。这种If电流可能在一定程度上有助于起搏电位的电发生。
