Sankaranarayanan S, Simasko S M
Department of VCAPP, College of Veterinary Medicine, Washington State University, Pullman, Wash., 99164-6520, USA.
Neuroendocrinology. 1998 Nov;68(5):297-311. doi: 10.1159/000054378.
Patch-clamp techniques were used in primary cultures of rat lactotropes and the rat pituitary clonal cell line GH3 to determine the population characteristics of spontaneous action potentials and the nature of the currents responsible for repolarization of spontaneous action potentials. Spontaneous action potentials were observed in 75% of lactotropes (74/99) and 80% of GH3 cells (42/51). Lactotropes exhibited broad and shallow action potentials (average duration 460 ms, peak -17 mV, slope of upstroke 0.5 mV/ms) compared to the GH3 cells which displayed narrow and tall action potentials (average duration 177 ms, peak -10 mV, slope of upstroke 1.6 mV/ms). Blockers of potassium currents were used to determine the role of specific potassium currents in the repolarization process. Spontaneous action potentials in lactotropes were largely unaffected by 4-aminopyridine (4AP), charybdotoxin, and apamin. Tetraethylammonium (TEA) caused only an small increase in peak amplitude and, in a subset of cells, a small increase in duration. In contrast, in GH3 cells, TEA, 4AP, charybdotoxin, and apamin all caused a significant increase in duration, while TEA and charybdotoxin also caused an increase in peak amplitude. Further, apamin caused a positive shift in the afterhyperpolarization voltage. In lactotropes, strong buffering of intracellular calcium with calcium chelators (EGTA or BAPTA) caused a profound increase in action potential duration. Thus, repolarization of action potentials in lactotropes is a calcium-dependent process, but unlike GH3 cells, is not mediated by calcium-dependent potassium currents, nor is it strongly influenced by voltage-dependent potassium currents.
采用膜片钳技术对大鼠促乳素细胞原代培养物和大鼠垂体克隆细胞系GH3进行研究，以确定自发动作电位的群体特征以及负责自发动作电位复极化的电流性质。在75%的促乳素细胞（74/99）和80%的GH3细胞（42/51）中观察到自发动作电位。与显示窄而高动作电位的GH3细胞相比，促乳素细胞表现出宽而浅的动作电位（平均持续时间460毫秒，峰值-17毫伏，上升斜率0.5毫伏/毫秒）（平均持续时间177毫秒，峰值-10毫伏，上升斜率1.6毫伏/毫秒）。使用钾电流阻滞剂来确定特定钾电流在复极化过程中的作用。促乳素细胞中的自发动作电位在很大程度上不受4-氨基吡啶（4AP）、蝎毒素和蜂毒明肽的影响。四乙铵（TEA）仅使峰值幅度略有增加，在一部分细胞中，持续时间略有增加。相比之下，在GH3细胞中，TEA、4AP、蝎毒素和蜂毒明肽均导致持续时间显著增加，而TEA和蝎毒素也导致峰值幅度增加。此外，蜂毒明肽使超极化后电压出现正向偏移。在促乳素细胞中，用钙螯合剂（乙二醇双四乙酸或1,2-双（2-氨基苯氧基）乙烷-N,N,N',N'-四乙酸）对细胞内钙进行强缓冲会导致动作电位持续时间大幅增加。因此，促乳素细胞中动作电位的复极化是一个钙依赖过程，但与GH3细胞不同，它不是由钙依赖钾电流介导的，也不受电压依赖钾电流的强烈影响。
