The stimulus-secretion coupling of amino acid-induced insulin release. IV. Ionic response to L-Leucine and L-Glutamine.
L-Glutamine enhances insulin release evoked by L-leucine in isolated rat pancreatic islets. The enhancing action of L-glutamine, which is a rapid but steadily increasing and not rapidly reversible phenomenon is not attributable to any major change in either K+ or Ca2+ outflow from the islet cells. It coincides with an apparent increase in Ca2+ inflow rate and, hence, with Ca accumulation in the islets. The initial ionic response to L-leucine is not qualitatively altered by the presence of L-glutamine. In their combined capacity to stimulate 45Ca net uptake in the islets, L-glutamine can be replaced by L-asparagine but not by L-glutamate, whereas L-leucine can be replaced by L-norvaline or L-isoleucine, but not by L-valine, glycine or L-lysine. Such a specificity is identical to that characterizing the effect of these various amino acids upon insulin release. It is postulated that the release of insulin evoked by the combination of L-leucine and L-glutamine involves essentially the same remodelling of ionic fluxes as that evoked by other nutrient secretagogues with, however, an unusual time course for the functional response to L-glutamine.
D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D002132:Calcium Radioisotopes; D005973:Glutamine / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism; D007930:Leucine / Q000494:pharmacology*; D010761:Phosphorus Radioisotopes; D011868:Radioisotopes; D051381:Rats; D012413:Rubidium; D013268:Stimulation, Chemical; D013997:Time Factors
D000596:Amino Acids; D002132:Calcium Radioisotopes; D007328:Insulin; D010761:Phosphorus Radioisotopes; D011868:Radioisotopes; D005973:Glutamine; D007930:Leucine; D012413:Rubidium