Nutrient insulin secretagogues decrease 45Ca2+ efflux from islet cells by a mechanism other than the inhibition of the Na+-Ca2+ countertransport.
The mechanism whereby nutrient insulin secretagogues decrease 45Ca2+ efflux from islet cells is controversial. It was studied with mouse islets perifused with Ca2+-free solutions. In the presence of Na+, glucose and ketoisocaproate inhibited 45Ca2+ efflux by about 50%. Substitution of choline+ salts for Na+ salts decreased the efflux rate by 45%, but did not prevent glucose from decreasing it further. Ketoisocaproate also inhibited 45Ca2+ efflux, but less markedly than in an Na+ medium. Omission of Na+ decreased the efflux rate even when it was already lowered by glucose or ketoisocaproate. It is thus clear that nutrient insulin secretagogues decrease 45Ca2+ efflux from islet cells by a mechanism other than the inhibition of the Na+-Ca2+ countertransport, possibly by increasing sequestration of the ion in cellular organelles.
D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002794:Choline / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D005260:Female; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007651:Keto Acids / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D015636:Magnesium Chloride; D051379:Mice; D012964:Sodium / Q000378:metabolism*
D007328:Insulin; D007651:Keto Acids; D015636:Magnesium Chloride; D004533:Egtazic Acid; C013082:alpha-ketoisocaproic acid; D012964:Sodium; D008274:Magnesium; D005947:Glucose; D002794:Choline; D002118:Calcium