Actively synthesizing beta-cells secrete preferentially after glucose stimulation.
To establish whether the heterogeneous secretion of glucose-stimulated beta-cells correlates with a different biosynthetic activity, we have studied the secretion and biosynthesis of the very same beta-cells by combining a hemolytic plaque assay with autoradiography. After a 10-min incubation in 2.8 mM glucose, 52 +/- 2% of dispersed rat beta-cells incorporated [3H] leucine into newly synthesized proteins, as revealed by autoradiographic labeling. When the incubation was performed in 16.7 mM glucose, larger (P less than 0.02) proportions (92 +/- 4%) of plaque-forming, i.e. insulin-secreting, and nonplaque-forming beta-cells (74 +/- 4%) were autoradiographically labeled. Labeled and unlabeled beta-cells were stimulated to secrete insulin during a 30-min incubation in 16.7 mM glucose, as revealed by the larger (P less than 0.001) formation of hemolytic plaques. Under these conditions, autoradiographically labeled beta-cells were recruited preferentially (P less than 0.01) and secreted more (P less than 0.04) than unlabeled beta-cells. Analogous observations were made with beta-cell pairs. Under glucose stimulation, pairs comprising two autoradiographically labeled beta-cells secreted more (P less than 0.004) than pairs comprising one or no labeled beta-cells. The data indicate that under glucose stimulation, 1) secreting and nonsecreting beta-cells increase protein biosynthesis; 2) biosynthetically active and inactive beta-cells increase insulin secretion; 3) beta-cells synthesizing new proteins release insulin preferentially; and 4) contact decreases the biosynthetic and secretory heterogeneity of beta-cells.
Bosco
D
D
Department of Morphology, University of Geneva Medical School, Switzerland.
Meda
P
P
D000818:Animals; D001345:Autoradiography; D005455:Fluorescent Antibody Technique; D005947:Glucose / Q000494:pharmacology*; D006462:Hemolytic Plaque Technique; D007328:Insulin / Q000096:biosynthesis / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007930:Leucine / Q000378:metabolism; D008297:Male; D008854:Microscopy, Electron; D051381:Rats; D011919:Rats, Inbred Strains
D007328:Insulin; D007930:Leucine; D005947:Glucose