Schüttler K, Boldt W
Martin Luther University Halle/Wittenberg, Julius Bernstein Institute of Physiology, Halle, GDR.
J Mol Cell Cardiol. 1989 Sep;21(9):901-9. doi: 10.1016/0022-2828(89)90758-x.
In rabbit papillary muscle, Ca-mediated action potentials (AP's) and maximum rate of rise (Vmax) were measured at 18 mM Ko. At steady state stimulation Vmax, overshoot and diastolic membrane potential were enhanced with increasing cycle length (CL) (from 8.7 to 14.1 V/s, from 25.1 to 34.1 mV, from -34.5 to -49.6 mV, respectively, between the CL of 1 and 60 s). AP-duration was only slightly prolonged (from 109 to 138 ms at 50% repolarization). 4-aminopyridine (5 mM) caused no or minor changes in the magnitude and CL-dependence of Vmax and overshoot. The AP-duration, however, was strongly prolonged due to a slower repolarization of the plateau phase with increasing CL. CsCl (20 mM) caused similar changes. Ca-mediated AP's elicited after a period of rest were found to be qualitatively similar to those which were obtained at increased steady state CL. Vmax of premature Ca-mediated AP's increased exponentially with the interval of stimulation, t, and was accurately described by: Vmax = A(1 - exp - (t-T)/tau). The K-channel blockers had no significant effect on the absolute refractory period, T, but increased the time constant, tau, from 123 to 166 ms. The restitution of AP-duration nicely matched this time course. The voltage dependence of membrane responsiveness showed a sigmoid shape, and was accurately described by: Vmax = A(1 + exp(V-Vs)/s)-1. The K-channel blockers increased s from 2.2 to 3.6 mV and shifted Vs from -26.8 to -22.1 mV.(ABSTRACT TRUNCATED AT 250 WORDS)
在兔乳头肌中，于18 mM钾离子浓度下测量钙介导的动作电位（AP）和最大上升速率（Vmax）。在稳态刺激下，随着周期长度（CL）增加（CL从1秒至60秒之间），Vmax、超射值和舒张期膜电位均增强（分别从8.7 V/s增至14.1 V/s、从25.1 mV增至34.1 mV、从 -34.5 mV增至 -49.6 mV）。动作电位持续时间仅略有延长（50%复极化时从109毫秒增至138毫秒）。4 - 氨基吡啶（5 mM）对Vmax和超射值的大小及CL依赖性无影响或仅有微小变化。然而，由于平台期复极化随CL增加而变慢，动作电位持续时间显著延长。氯化铯（20 mM）引起类似变化。发现休息一段时间后引发的钙介导动作电位在性质上与在增加的稳态CL下获得的动作电位相似。过早钙介导动作电位的Vmax随刺激间隔时间t呈指数增加，并且可精确描述为：Vmax = A(1 - exp - (t - T)/tau)。钾通道阻滞剂对绝对不应期T无显著影响，但使时间常数tau从123毫秒增至166毫秒。动作电位持续时间的恢复与该时间进程良好匹配。膜反应性的电压依赖性呈S形，并且可精确描述为：Vmax = A(1 + exp(V - Vs)/s)-1。钾通道阻滞剂使s从2.2 mV增至3.6 mV，并使Vs从 -26.8 mV移至 -22.1 mV。（摘要截断于250字）
