Cobalt inhibition of insulin release: evidence for an action not related to Ca2+ uptake.
Insulin release, Ca2+ fluxes, and adenosine 3',5'-cyclic monophosphate (cAMP) levels were measured under various conditions to test the selectivity of cobalt (Co2+) actions in pancreatic islets. Insulin release was measured simultaneously either with 45Ca2+ uptake or 45Ca2+ efflux from rat islets maintained 2 days in tissue culture. Glucose (16.7 mM)-stimulated insulin release was inhibited by Co2+ (0.25, 0.5 mM) without concomitant inhibition of glucose-stimulated 45Ca2+ uptake. At higher concentrations of Co2+ (1.0, 2.5 mM) glucose- as well as K+-stimulated insulin release were inhibited in parallel with 45Ca2+ uptake. In the presence or the absence of external Ca2+, Co2+ (0.5 mM) also decreased 3-isobutyl-1-methylxanthine-stimulated insulin release, which does not depend on the stimulation of Ca2+ uptake. Co2+ did not alter islet cAMP levels. Co2+ also did not affect the unidirectional basal 45Ca2+ efflux measured in the absence of Ca2+ but completely overcame the stimulated 45Ca2+ efflux evoked by the removal of external Mg2+. Under the latter conditions, 50, but not 5 microM verapamil, decreased the stimulated 45Ca2+ efflux. It is concluded that Co2+ is able to inhibit insulin release and lower Ca2+ efflux without apparent interference with Ca2+ uptake. This suggests that Co2+, in addition to its well-known inhibition of Ca2+ uptake, may exert its action at a distal step in the insulin release process.
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003035:Cobalt / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014700:Verapamil / Q000494:pharmacology
D007328:Insulin; D003035:Cobalt; D014700:Verapamil; D000242:Cyclic AMP; D005947:Glucose; D011188:Potassium; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine