Outward potassium currents of supraoptic magnocellular neurosecretory cells isolated from the adult guinea‐pig

Publisher Website
Google Scholar
Abstract
1 Several types of whole‐cell outward K+ current recorded from magnocellular neurosecretory cells (MNCs) dissociated from the supraoptic nucleus of the adult guinea‐pig were identified on the basis of their voltage dependence, kinetics, pharmacology and Ca2+ dependence. 2 The predominant K+ current evoked from a holding potential of −40 mV was slowly activating, long‐lasting, tetraethylammonium (TEA) sensitive and showed little steady‐state inactivation. Also, this current was reduced by extracellular Cd2+. These data suggest that in supraoptic MNCs classical Ca2+‐insensitive, delayed rectifier channels (Kv) and Ca2+‐sensitive, non‐inactivating channels (KCa) both contribute to the sustained current. 3 A transient, low‐threshold K+ current, which was 4‐aminopyridine (4‐AP) sensitive and showed significant steady‐state inactivation, was evoked along with the sustained current from a holding potential of −90 mV. Based on these characteristics, this current corresponds to the A‐current (IK(A)) described in other neurons. 4 I K(A) was activated when Ca2+ influx was blocked or when Ca2+ was absent from the extracellular medium, suggesting that Ca2+ influx is not necessary for activation of the current. 5 In many recordings, a transient 4‐AP‐insensitive outward current was evoked from a holding potential of −40 mV. This high‐threshold transient K+ current was abolished by extracellular Cd2+ or TEA and was absent when extracellular Ca2+ was replaced by Sr2+, suggesting that it is a transient Ca2+‐dependent K+ current. 6 We conclude that the presence of multiple types of K+ current may, in part, underlie the complex firing patterns of oxytocinergic and vasopressinergic MNCs.