A G protein-activated K+ current in bovine adrenal chromaffin cells: possible regulatory role in exocytosis

SD Cannon, SP Wilson and KB Walsh

Department of Pharmacology, University of South Carolina School of Medicine, Columbia 29208.

Guanine nucleotide binding proteins (G proteins) act as signal transducers between membrane receptors and ion channels. In the present study, the whole-cell arrangement of the patch clamp technique was used to examine the effect of G proteins on K+ channels in cultured bovine adrenal chromaffin cells. Internal dialysis of chromaffin cells with guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) or external application of AIF-4, to stimulate G proteins, resulted in a voltage- dependent increase in the amplitude of the outward K+ currents. The half-maximal voltage required for activation of the currents was shifted by -16 mV in the presence of GTP gamma S. The augmentation in the K+ currents was accompanied by the appearance of a fast component of current activation measured at potentials positive to 0 mV. The GTP gamma S-sensitive current could not be detected when internal K+ was replaced with Cs+ and was reversibly inhibited by tetraethylammonium (IC50, 2 mM). In contrast, the scorpion venom charybdotoxin (50 nM) and the bee venom apamin (250 nM) only slightly reduced the K+ currents during stimulation by GTP gamma S and did not alter the activation kinetics. In addition, the GTP gamma S-sensitive K+ current could be activated in the absence of internal Ca2+ and when the inward Ca2+ current was inhibited with CdCl2. Treatment of the chromaffin cells with fluoride decreased nicotine-evoked secretion of catecholamines in a concentration-dependent manner. Thus, bovine chromaffin cells contain a G protein-stimulated K+ channel that may play a regulatory role in secretagogue-mediated exocytosis.

Volume 45, Issue 1, pp. 109-116, 01/01/1994
Copyright © 1994 by American Society for Pharmacology and Experimental Therapeutics