A G protein-activated K+ current in bovine adrenal chromaffin cells: possible regulatory role in exocytosis.
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.
Cannon
S D
SD
Department of Pharmacology, University of South Carolina School of Medicine, Columbia 29208.
Wilson
S P
SP
Walsh
K B
KB
D000311:Adrenal Glands / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D017607:Aluminum Compounds / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D002837:Chromaffin Granules; D005089:Exocytosis / Q000502:physiology*; D005459:Fluorides / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D007700:Kinetics; D015221:Potassium Channels / Q000378:metabolism*
D017607:Aluminum Compounds; D002395:Catecholamines; D015221:Potassium Channels; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D019204:GTP-Binding Proteins; D005459:Fluorides; D002118:Calcium; C032311:aluminum fluoride