Akiyama T, Fozzard H A
Am J Physiol. 1979 Jan;236(1):C1-8. doi: 10.1152/ajpcell.1979.236.1.C1.
The atrioventricular (AV) node is thought to have a slow ionic channel. These experiments were designed to measure the relative contributions of Na and Ca ions to inward currents in the AV nodal cells of rabbit heart superfused with Tyrode solution. The effects of tetrodoxin (TTX), Mn2+, and verapamil observed in this study were in agreement with reports by others. The overshoot of AV nodal (N) cells was related to external Ca, with a slope of 12 mV/decade, unchanged by addition of TTX. Similar dependence of overshoot on external Na was seen, with a slope of 20 mV/decade. The slope did not change on addition of TTX. Total removal of either Na or Ca from the solution abolished excitability. Using a constant field equation, we estimated relative permeability (P) of the membrane at the time of maximal overshoot to be PCa/PNa congruent to 60 similar to or approximately 100 and PK/PNa congruent to 1. Relative contributions of these ions to the currents were estimated as ICa congruent to 17%, INa congruent to 33% (inward currents), and IK congruent to 50% (outward current). In conclusion, AV nodal cells have "slow inward-current channels" that are selective for Ca over Na ions.
房室（AV）结被认为具有缓慢的离子通道。这些实验旨在测量钠和钙离子对灌流有台氏液的兔心脏房室结细胞内向电流的相对贡献。本研究中观察到的河豚毒素（TTX）、锰离子和维拉帕米的作用与其他人的报告一致。房室结（N）细胞的超射与细胞外钙有关，斜率为12 mV/十倍浓度变化，添加TTX后不变。超射对细胞外钠也有类似的依赖性，斜率为20 mV/十倍浓度变化。添加TTX后斜率不变。溶液中完全去除钠或钙会消除兴奋性。使用恒定场方程，我们估计在最大超射时膜的相对通透性（P）为PCa/PNa约为60至100，PK/PNa约为1。这些离子对电流的相对贡献估计为ICa约为17%，INa约为33%（内向电流），IK约为50%（外向电流）。总之，房室结细胞具有对钙离子比对钠离子更具选择性的“缓慢内向电流通道”。
