AJP - Cell Physiology, Vol 261, Issue 2 C218-C223, Copyright © 1991 by American Physiological Society
Blockade by lithium ions of potassium channels in rat anterior pituitary cells
M. Kato, P. M. Lledo and J. D. Vincent
Laboratoire de Neurobiologie des Comportements, Institut National de la Sante, et de la Recherche Medicale Unite 176, Bordeaux, France.
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.
