Somatostatin increases voltage-dependent potassium currents in rat somatotrophs.
To study the modulatory effects of somatostatin on membrane K+ currents, whole cell voltage-clamp recordings were performed on identified rat somatotrophs in primary culture. In the presence of Co2+ (2 mM) and tetrodotoxin (1 microM) in the bath solution to block Ca2+ and Na+ inward currents, two types of voltage-activated K+ currents were identified on the basis of their kinetics and pharmacology. First, a delayed rectifier K+ current (IK) had a threshold of -20 mV, did not decay during voltage steps lasting 300 ms, and was markedly attenuated by extracellular application of tetraethylammonium (TEA, 10 mM). Second, a transient outward K+ current (IA) was activated at -40 mV (from a holding potential of -80 mV) and persisted despite the presence of TEA. This IA was blocked by 4-aminopyridine (2 mM). Somatostatin (10 nM) increased IK by 75% and IA by 45% without obvious effects on steady-state voltage dependency of activation or inactivation, and these effects were reversible. This increase in K+ currents may contribute in part to the inhibitory effect of somatostatin on growth hormone release.
Chen
C
C
Institute National de la Santé et de la Recherche Medicale U. 176, Bordeaux, France.
Zhang
J
J
Vincent
J D
JD
Israel
J M
JM
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D003035:Cobalt / Q000494:pharmacology; D004594:Electrophysiology / Q000379:methods; D005071:Evoked Potentials / Q000187:drug effects; D007700:Kinetics; D008297:Male; D010902:Pituitary Gland / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013004:Somatostatin / Q000494:pharmacology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D003035:Cobalt; D013004:Somatostatin; D019789:Tetraethylammonium; D015761:4-Aminopyridine; C018021:cobaltous chloride