Gurkovskaia A V, Shuba M F, Buryĭ V A
Fiziol Zh SSSR Im I M Sechenova. 1983 Aug;69(8):1065-73.
Depolarization of the rabbit pulmonary artery smooth muscle cells over critical level (5-7 mV) by outward current or high K+ solution application produced contraction proportional to the depolarization. High K+ solution produced an initial spike on the rising phase of depolarization followed by subsequent phasic contraction amplitude of which was lower than that of the tonic one. Anelectrotonic repolarization of smooth muscle cells by means of inward current in high K+ solution was usually followed by spontaneous AP generation and subsequent phasic contractions which were summed and increased total contractile tension. If the spontaneous APs were not generated anelectrotonic repolarization was followed by relaxation of the smooth muscle proportional to the extent of repolarization. AP in this case could be evoked by electrical stimulation. Experiments with Ca--free solution and application of Ca and K-channel blockers suggest the existence of two types of voltage--dependent Ca--channels in the membrane of these smooth muscle cells: fast inactivated responsible for AP generation and phasic contraction, and slow noninactivated responsible for tonic contractions, dependent on the transmembrane potential. In physiological conditions, a functional role of the fast Ca channels is limited due to early activation of K-conductance which is comparatively large in these smooth muscle cells and suppresses AP generation.
通过外向电流或应用高钾溶液使兔肺动脉平滑肌细胞去极化超过临界水平（5 - 7毫伏）时，会产生与去极化程度成比例的收缩。高钾溶液在去极化上升阶段产生一个初始尖峰，随后是相位收缩幅度，其低于强直收缩幅度。在高钾溶液中通过内向电流使平滑肌细胞进行电紧张性复极化后，通常会自发产生动作电位（AP）以及随后的相位收缩，这些收缩会叠加并增加总收缩张力。如果未自发产生动作电位，电紧张性复极化后平滑肌会按复极化程度成比例地松弛。在这种情况下，动作电位可通过电刺激诱发。无钙溶液实验以及钙通道和钾通道阻滞剂的应用表明，这些平滑肌细胞膜中存在两种电压依赖性钙通道：快速失活型负责动作电位的产生和相位收缩，慢速非失活型负责强直收缩，其依赖于跨膜电位。在生理条件下，快速钙通道的功能作用受到限制，这是由于这些平滑肌细胞中钾电导的早期激活，其相对较大并抑制动作电位的产生。
