A role for polyamines in stimulus-secretion coupling in the pancreatic beta-cell.

Measurement of the content of polyamines in pancreatic islets indicated that no significant change in their concentration took place during glucose-stimulated insulin release. The finding, together with the absence of any effect of alpha-difluoromethylornithine on glucose-stimulated insulin release suggested that rapid synthesis of polyamines is not involved in stimulus-secretion coupling in the beta-cell. The concentration of polyamines found in islets were high enough for them to act as substrates for the Ca2+-dependent islet transglutaminase during insulin release. This was further demonstrated by the ability of islet transglutaminase to incorporate [14C]putrescine into proteins from islet homogenates and by the demonstration of an increase in the covalent incorporation of [14C]putrescine into the proteins of intact islets following their challenge with glucose. Unlike monoamine substrates of transglutaminase, putrescine failed to effectively inhibit insulin release when its intracellular concentration was increased. A role for polyamines in the secretory process through their incorporation into islet proteins is suggested.