Ruiz-Ceretti E, Zumino A P
Circ Res. 1976 Sep;39(3):326-36. doi: 10.1161/01.res.39.3.326.
In the perfused rabbit heart,the upstroke of the transmembrane action potential of fibers of the atrioventricular (AV) node presents two distinct components. The first depends strongly on extracellular sdoium concentration, but the degree to which it is activated is influenced by extracellular calcium, as indicated by the correlation between its Vmax and [Ca2+]0. The second component depends on calcium and sodium concentrations and is blocked by Mn ions. An analysis comparing action potentials from atrial (A), atrionodal (AN), and nodal (N) fibers shows that the second component of the upstroke of the action potential contributes 12%, 27%, and 34% to the total depolarization. The results suggest that the upstroke of the nodal action potential results from the activation of two inward currents, as in ordinary cardiac fibers. We postulate that (1) the degree of steady state inactivation of gNa is larger in N than in A fibers because of the low resting potential of the former, and (2) the contribution of the second channel to the upstroke depends on the time course of the previous depolarization and the potential level at which this component is activated.
在灌注兔心脏中，房室（AV）结纤维跨膜动作电位的上升支呈现出两个不同的成分。第一个成分强烈依赖于细胞外钠浓度，但其激活程度受细胞外钙的影响，这可由其最大上升速率（Vmax）与细胞外钙离子浓度（[Ca2+]0）之间的相关性表明。第二个成分依赖于钙和钠浓度，并被锰离子阻断。一项比较心房（A）、房结区（AN）和结区（N）纤维动作电位的分析表明，动作电位上升支的第二个成分对总去极化的贡献分别为12%、27%和34%。结果表明，结区动作电位的上升支是由两种内向电流的激活引起的，这与普通心肌纤维的情况相同。我们推测：（1）由于N纤维静息电位较低，其钠通道（gNa）的稳态失活程度比A纤维更大；（2）第二个通道对动作电位上升支的贡献取决于前一次去极化的时间进程以及该成分被激活时的电位水平。
