title: Insulin secretion in aging: studies with sequential gating of secretion vesicle margination and lysis.
abstract: A new sequential gating perifusion technique was employed to investigate secretion vesicle margination and granule lysis in islets isolated from 2- and 18-month-old Fischer 344 rats. The technique is based on sequential perifusion (periods A, B, and C) of isolated islets with glucose (30, 165, or 300 mg/dl) in the presence of sodium isethionate, an inhibitor of granule lysis, followed thereafter by trifluoperazine, an inhibitor of secretion vesicle margination, and glucose (300 mg/dl) or isobutylmethylxanthine (IBMX; 400 microM). When glucose was employed during period A to marginate secretion vesicles to the plasma membrane, subsequent glucose- and IBMX-induced insulin release (period C) was depressed in islets from 18-month-old rats [maximal increase above the basal rate of release (delta max), 9 +/- 2 nU/micron X min] compared to that in the 2-month-old animals (delta max, -19 +/- 3 nU/micron X min). With glyburide (400 microM) used to induce secretion vesicle margination, glucose- and IBMX-induced insulin release was the same in young and old animals (delta max, 14 +/- 3 and 15 +/- 3 nU/micron X min, respectively). Insulin release was then studied as a function of secretion vesicle margination at the plasma membrane by measuring somatostatin (SRIF) receptor recruitment. The islets from older animals must be stimulated with 300 mg/dl glucose to attain the same level of SRIF binding as in islets isolated from younger animals stimulated with 150-165 mg/dl glucose. Insulin release per unit SRIF binding was identical in young and old animals (65 and 69 nU/liter fmol SRIF binding), indicating normal lysis of marginated secretion granules. These studies implicate glucose-induced secretion vesicle margination as the site of impairment in age-related insulin release.
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000375:Aging; D000818:Animals; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000502:physiology*; D005947:Glucose / Q000494:pharmacology; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051381:Rats; D011916:Rats, Inbred F344; D013004:Somatostatin / Q000378:metabolism
chemical_list: D007328:Insulin; D013004:Somatostatin; D005947:Glucose; D015056:1-Methyl-3-isobutylxanthine