Blockade by lithium ions of potassium channels in rat anterior pituitary cells.
Extracellular Li+ has been known to facilitate the basal secretion of growth hormone from anterior pituitary cells and of catecholamine from chromaffin cells. In both cases, the intracellular accumulation of Li+ seems to be the prerequisite, and the presence of extracellular Ca2+ is indispensable. In this series of experiments, we examined whether Li+ blocked K+ currents by using primary cultured anterior pituitary cells from male rats. K+ currents were measured in the whole cell configuration of the patch-clamp technique. Extracellular Li+ (140 mM) suppressed both the delayed rectifier K+ current (IK) and the transient outward K+ current to 71 and 69% of control, respectively, in a reversible manner. IK elicited by a voltage step to +70 mV from holding potential of -70 mV was suppressed by 32.5 mM internal Li+ to 28% of control. Half-maximal suppression of K+ conductance by internal Li+ was 16 mM. Furthermore, Ca(2+)-channel blocker methoxyverapamil potently suppressed Li(+)-induced growth hormone secretion. From these results we propose that the blockade by Li+ of K+ channels could depolarize the cells and activate Ca2+ channels, thereby promoting the influx of Ca2+ and hormone secretion as a mechanism of Li(+)-induced hormone secretion.
Kato
M
M
Laboratoire de Neurobiologie des Comportements, Institut National de la Santé, et de la Recherche Médicale Unité 176, Bordeaux, France.
Lledo
P M
PM
Vincent
J D
JD
D000818:Animals; D004594:Electrophysiology; D005711:Gallopamil / Q000494:pharmacology; D013006:Growth Hormone / Q000378:metabolism; D007477:Ions; D008094:Lithium / Q000494:pharmacology*; D008297:Male; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D015221:Potassium Channels / Q000502:physiology*; D051381:Rats
D007477:Ions; D015221:Potassium Channels; D005711:Gallopamil; D013006:Growth Hormone; D008094:Lithium