Chen C, Heyward P, Zhang J, Wu D, Clarke I J
Prince Henry's Institute of Medical Research, Clayton, Australia.
Neuroendocrinology. 1994 Jan;59(1):1-9. doi: 10.1159/000126631.
Sheep somatotroph-enriched cultures were obtained by means of enzyme dissociation and Percoll gradient separation. Nystatin-perforated-whole-cell recordings were performed on post-recording-identified somatotrophs after 4-14 days in vitro. Using Ca(2+)-free, tetrodotoxin-containing (1 microM) bath solution and K+ electrode solution, three types of voltage-dependent K+ currents were recorded as inward rectifying, outward transient and outward delayed rectifying K+ currents. The inward rectifying K+ current was very small at physiological extracellular K+ concentrations (5 mM) and enhanced by increasing the K+ concentration in the bath to 55 mM; it was blocked by tetraethylammonium (2 mM) but not by 4-aminopyridine (5 mM). A transient outward K+ current appeared at -50 mV and was selectively diminished by 4-aminopyridine (2 or 4 mM). A delayed rectifying outward K+ current was observed when the membrane potential was depolarized to -20 mV and was blocked by tetraethylammonium (2 mM) but not 4-aminopyridine (4 mM). Application of 4-aminopyridine but not tetraethylammonium (up to 5 mM) depolarized the cell membrane potential recorded under current clamp conditions and triggered action potentials when the bath solution contained Ca2+ (2 mM) but not tetrodotoxin. The intracellular Ca2+ concentration was increased by 4-aminopyridine as was growth hormone release. Therefore, the 4-aminopyridine-sensitive transient outward K+ current appears to be important in the determining the resting potential of ovine somatotrophs and plays a major role in regulating basal intracellular Ca2+ concentration and growth hormone secretion.
通过酶解离和Percoll梯度分离获得富含绵羊生长激素分泌细胞的培养物。在体外培养4 - 14天后，对记录后鉴定的生长激素分泌细胞进行制霉菌素穿孔全细胞记录。使用无钙、含河豚毒素（1 microM）的浴液和钾电极溶液，记录到三种类型的电压依赖性钾电流，即内向整流钾电流、外向瞬时钾电流和外向延迟整流钾电流。内向整流钾电流在生理细胞外钾浓度（5 mM）时非常小，当浴液中钾浓度增加到55 mM时增强；它被四乙铵（2 mM）阻断，但不被4 - 氨基吡啶（5 mM）阻断。外向瞬时钾电流在 - 50 mV时出现，并被4 - 氨基吡啶（2或4 mM）选择性减弱。当膜电位去极化到 - 20 mV时观察到外向延迟整流钾电流，它被四乙铵（2 mM）阻断，但不被4 - 氨基吡啶（4 mM）阻断。应用4 - 氨基吡啶而非四乙铵（高达5 mM）可使电流钳条件下记录的细胞膜电位去极化，并在浴液中含有钙离子（2 mM）但不含河豚毒素时触发动作电位。4 - 氨基吡啶可增加细胞内钙离子浓度以及生长激素释放。因此，4 - 氨基吡啶敏感的外向瞬时钾电流似乎在决定绵羊生长激素分泌细胞的静息电位中起重要作用，并在调节基础细胞内钙离子浓度和生长激素分泌中起主要作用。
