Leucine induces initial lowering of cytoplasmic Ca2+ in pancreatic beta-cells without concomitant inhibition of insulin release.
The early effects of glucose and leucine on cytoplasmic Ca2+ and insulin release were compared in suspensions of cells prepared by dispersal of the beta-cell-rich pancreatic islets of ob/ob-mice. Adequate temporal resolution was achieved by continuously recording the 340/380 nm fluorescence excitation ratio from cells loaded with the Ca2+ indicator fura-2 and measuring insulin in the perifusate from cells mixed with polyacrylamide beads. Raising the glucose concentration from 3 to 20 mM resulted in concomitant reductions of cytoplasmic Ca2+ and insulin release during the first minute. Whereas 10 mM leucine was as efficient as glucose in inducing temporary lowering of cytoplasmic Ca2+, this amino acid did not depress insulin release. It is concluded that the initial decrease of cytoplasmic Ca2+ is a phenomenon coupled to stimulation of the metabolism. The leucine-induced lowering of Ca2+ may essentially reflect changes in cytoplasmic pools other than in a peripheral one regulating insulin release.
Lund
P E
PE
Department of Medical Cell Biology, University of Uppsala, Sweden.
Gylfe
E
E
Hellman
B
B
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D007930:Leucine / Q000494:pharmacology*; D051379:Mice; D008820:Mice, Obese; D013050:Spectrometry, Fluorescence
D007328:Insulin; D007930:Leucine; D005947:Glucose; D002118:Calcium