Specificity of divalent cation requirement for insulin release. Effects of strontium.
Isolated pancreatic islets of rats were used to investigate whether Sr2+ can effectively replace Ca2+ in sustaining insulin release. Insulin secretion in response to glucose, potassium and tolbutamide was lower in a Sr2+ than in a Ca2+ medium, even at the optimum concentration of 2.5 mmol/l. The amplitude of the second phase of glucose-induced release was inversely related to the duration of Ca2+ replacement by Sr2+. The insulinotropic effect of glucose was suppressed by Co2+ and D600 in a Sr2+ medium and also reduced by addition of Sr2+ itself to a Ca2+ medium. Glucose uptake, glucose utilization and K-permeability in islet cells were not altered by Sr2+ substitution for Ca2+. The basal uptake of Sr2+ was lower than that of Ca2+, but was increased by glucose or high K+, Co2+ and Ca2+ inhibited Sr2+ uptake more markedly than Co2+ and Sr2+ inhibited Ca2+ uptake. High glucose reduced Sr2+ efflux from islet cells less markedly than Ca2+ efflux. These results show that Sr2+ is less effective than Ca2+ in sustaining insulin release and suggest that the difference between both cations are due to non identical membrane transport and unequal activation of later steps of the stimulus-secretion coupling.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002413:Cations, Divalent; D003035:Cobalt / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D005711:Gallopamil / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D013324:Strontium / Q000378:metabolism / Q000494:pharmacology*; D014044:Tolbutamide / Q000494:pharmacology
D002413:Cations, Divalent; D007328:Insulin; D005711:Gallopamil; D003035:Cobalt; D004533:Egtazic Acid; D014044:Tolbutamide; D005947:Glucose; D011188:Potassium; D002118:Calcium; D013324:Strontium