Fast insulin secretion reflects exocytosis of docked granules in mouse pancreatic B-cells.

摘要: A readily releasable pool (RRP) of granules has been proposed to underlie the first phase insulin secretion. In present study we combined electron microscopy, secretion measurements and recordings cell capacitance in an attempt define this ultrastructurally. Mouse pancreatic B-cells contain approximately 9,000 granules, which 7% are docked below plasma membrane. The number was reduced by 30% (200 granules) during 10 min stimulation with high K+. This stimulus depolarized -10 mV, elevated cytosolic [Ca2+] ([Ca2+](i)) from a basal concentration 130 nM peak 1.3 microM released 0.5 ng insulin/islet, corresponding 200-300 granules/cell. Ca2+ transient decayed towards prestimulatory within 200 s, presumably reflecting channel inactivation. Renewed K+ failed stimulate when applied absence glucose. size RRP, derived measurements, is similar that estimated increase elicited photolytic release caged Ca2+. We propose RRP represents subset replenishment can be accounted for largely chemical modification already place or situated close