Outward potassium currents of supraoptic magnocellular neurosecretory cells isolated from the adult guinea-pig.
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 Ca(2+)-insensitive, delayed rectifier channels (KV) and Ca(2+)-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. IK(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 Ca(2+)-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.
Hlubek
M D
MD
Department of Pharmacology and Toxicology, Michigan State University, East Lansing 48824-1317, USA.
Cobbett
P
P
D015761:4-Aminopyridine / Q000494:pharmacology; D000367:Age Factors; D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D004594:Electrophysiology; D006168:Guinea Pigs; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007700:Kinetics; D008297:Male; D009490:Neurosecretory Systems / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000502:physiology; D013495:Supraoptic Nucleus / Q000166:cytology* / Q000378:metabolism; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D002104:Cadmium; D019789:Tetraethylammonium; D015761:4-Aminopyridine; D011188:Potassium; D002118:Calcium