STIMULATION OF INSULIN RELEASE FROM PERMEABILIZED HIT-T15 CELLS BY A SYNTHETIC PEPTIDE CORRESPONDING TO THE EFFECTOR DOMAIN OF THE SMALL GTP-BINDING PROTEIN RAB3

A synthetic peptide (rab3AL) corresponding to the effector domain of rab3, a small GTP-binding protein, stimulated basal and potentiated Ca2+- as well as GTPgammaS-evoked insulin secretion about 2-fold from streptolysin-0 permeabilized HIT cells. This effect was specific, since the analogous peptides of ras or rab1 did not affect the exocytotic event. The more than additive effect of rab3AL on Ca2+ or GTPgammaS stimulation indicates a distinct mode of action of the peptide. The partial loss of cytosolic proteins from permeabilized cells was accompanied by a faster run-down of the secretory response to Ca2+ than the one to GTPgammaS. The persistent effect of rab3AL under these conditions points to a membrane localization of its target. These results suggest that rab3 and its effector are involved in the regulation of insulin secretion.