Enhanced activation of phospholipase C and insulin secretion from islets incubated in fatty acid–free bovine serum albumin

Abstract

Incubation in 100 μmol/L fatty acid–free bovine serum albumin (FAF-BSA) significantly amplifies insulin secretion from isolated, perifused rat islets. When compared with the responses of control islets incubated in 100 μmol/L radioimmunoassay-grade BSA, insulin secretion rates were increased 2- to 3-fold when these islets were stimulated with 10 mmol/L glucose alone or with the combination of 10 mmol/L glucose, 15 mmol/L KCl, and 100 μmol/L diazoxide. These amplified secretory responses were paralleled by significant increases in the phospholipase C (PLC) activation monitored by fractional increases in 3H-inositol efflux from these same islets. Amplified PLC responses were also observed with the cholinergic agonist carbachol (50 μmol/L). No differences in the secretory responses to the protein kinase C activator phorbol 12-myristate 13-acetate (200 nmol/L) could be detected between control and FAF-BSA–pretreated rat islets. Mouse islets were also immune to the amplifying impact of this treatment protocol. These findings demonstrate that short-term incubation in FAF-BSA significantly augments the activation of PLC in rat islets by a number of agonists. This proximal event provides the impetus for the distal activation of protein kinase C. If applicable to human islets, this manipulation may provide a mechanism to enhance the secretory responses from islets destined for transplantation, thus improving their in vivo secretory capacity.