Endothelin stimulates 86Rb efflux in rat glioma C6-Bu-1 cells.
Endothelin-1 (ET) elevates intracellular calcium ([Ca2+]i) and increased [Ca2+]i has been associated with K+ efflux. Therefore, we investigated ET stimulation of K+ efflux in rat glioma C6-BU-1 cells. K+ efflux was measured by monitoring the release of 86Rb+ from cells pre-loaded with 86RbCl. ET stimulated 86Rb+ efflux with an EC50 of 5.9 nM. ET-stimulated 86Rb+ efflux was insensitive to Ca2+ channel blockade, however it was reduced by 68% in Ca(2+)-free buffer, suggesting a sizable dependence on an extracellular source of Ca2+ influx through non voltage-operated Ca2+ channels. ET-stimulated 45Ca2+ efflux slightly preceded 86Rb+ efflux, again suggesting the presence of Ca2+ dependent K+ channels. ET-stimulated 86Rb+ efflux was insensitive to glyburide suggesting that efflux is not through ATP-sensitive K+ channels. ET-stimulated 86Rb+ efflux was insensitive to pertussis toxin (PTX) pre-treatment. Pre-incubation with the protein kinase C (PKC) inhibitor, staurosporine, inhibited 86Rb+ efflux by 66%, suggesting the involvement of PKC activation in ET-mediated 86Rb+ efflux. In summary, in C6-BU-1 cells, ET stimulates Ca2+ dependent K+ efflux which is mediated in part by protein kinase C activation, but not a PTX sensitive G-protein, nor through an ATP-sensitive K+ channel. These data extend the intracellular mechanisms initiated by ET to include Ca2+ dependent K+ efflux in glial cells and further support a neuromodulatory role for ET.
Gleason
M M
MM
Department of Pharmacology, SmithKline Beecham Pharmaceuticals, King of Prussia, PA 19406-0939.
Griffin
E C
EC
Nambi
P
P
Aiyar
N
N
D000470:Alkaloids / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004110:Diltiazem / Q000494:pharmacology; D016232:Endothelins / Q000494:pharmacology*; D005910:Glioma / Q000378:metabolism*; D005905:Glyburide / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D037342:Pertussis Toxin; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D012413:Rubidium / Q000378:metabolism*; D019311:Staurosporine; D014407:Tumor Cells, Cultured; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D000470:Alkaloids; D016232:Endothelins; D015221:Potassium Channels; D010566:Virulence Factors, Bordetella; D037342:Pertussis Toxin; D011493:Protein Kinase C; D004110:Diltiazem; D019311:Staurosporine; D009543:Nifedipine; D012413:Rubidium; D011188:Potassium; D005905:Glyburide; D002118:Calcium