Distinct effects of various amino acids on 45Ca2+ fluxes in rat pancreatic islets.
The effects of three types of amino acids on 45Ca2+ fluxes in rat pancreatic islets have been compared. Alanine, a non-insulinotropic neutral amino acid, transported with Na+, increased 45Ca2+ efflux in the presence or in the absence of extracellular Ca2+, but not in the absence of Na+. Its effects in Na+-solutions were practically abolished by 7 mM-glucose. Alanine slightly stimulated 45Ca2+ influx (5 min uptake) only when Na+ was present. Two insulinotropic cationic amino acids (arginine and lysine) triggered similar changes in 45Ca2+ efflux. They accelerated the efflux in the presence of Ca2+ and inhibited the efflux in a Ca2+-free medium, whether glucose was present or not. In an Na+-free Ca2+-medium, arginine and lysine markedly accelerated 45Ca2+ efflux, but this effect was suppressed by 7 mM-glucose. Arginine stimulated 45Ca2+ influx irrespective of the presence or absence of glucose and Na+. Leucine, a neutral insulinotropic amino acid well metabolized by islet cells, inhibited 45Ca2+ efflux from the islets in a Ca2+-free medium; this effect was potentiated by glutamine. In the presence of Ca2+ and Na+, leucine was ineffective alone, but triggered a marked increase in 45Ca2+ efflux when combined with glutamine. In an Na+-free Ca2+-medium, leucine accelerated 45Ca2+ efflux to the same extent with or without glutamine. Leucine also stimulated 45Ca2+ influx in the presence or in the absence of Na+, but its effects were potentiated by glutamine only in the presence of Na+. The results show that amino acids of various types cause distinct changes in 45Ca2+ fluxes in pancreatic islets. Certain of these changes involve an Na+-mediated mobilization of cellular Ca2+ from sequestering sites where glucose appears to exert an opposite effect.
D000409:Alanine / Q000494:pharmacology; D000596:Amino Acids / Q000494:pharmacology*; D000818:Animals; D001120:Arginine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007930:Leucine / Q000494:pharmacology; D008239:Lysine / Q000494:pharmacology; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000494:pharmacology
D000596:Amino Acids; D001120:Arginine; D012964:Sodium; D007930:Leucine; D005947:Glucose; D008239:Lysine; D000409:Alanine; D002118:Calcium