Regulation of immunoreactive-insulin release from a rat cell line (RINm5F)

Abstract

An insulin-producing cell line, RINm5F, derived from a rat insulinoma was studied. The cellular content of immunoreactive insulin was 0.19 pg/cell, which represents .apprx. 1% of the insulin content of native rat .beta.-cells, whereas that of immunoreactive glucagon and somatostatin was 5-6 orders of magnitude less than that of native .alpha.- or .delta.-cells, respectively. RINm5F cells released 7-12% of their cellular immunoreactive-insulin content at 2.8 mM-glucose during 60 min in Krebs-Ringer bicarbonate buffer. Glucose utilization was increased by raising glucose from 2.8 to 16.7 mM. There was, however, no stimulation of immunoreactive-insulin release even when glucose was increased from 2.8 to 33.4 mM. A small stimulation of release was found when glucose was raised from 0 to 2.8 mM. Glyceraldehyde stimulated the release of immunoreactive insulin in a dose-dependent manner. At 20 mM, leucine or arginine stimulated release at 2.8 mM-glucose. Raising intracellular cAMP by glucagon or 3-isobutyl-1-methylxanthine stimulated release at 2.8 mM-glucose with no additional stimulation at 16.7 mM-glucose. Stimulation of immunoreactive-insulin release by K+ was dose-related between 2 and 30 mM. Another depolarizing agent, ouabain, also stimulated release. Adrenaline (epinephrine) inhibited both basal (2.8 mM-glucose) release and that simulated by 30 mM-K+. Raising Ca2+ from 1 to 3 mM stimulated immunoreactive-insulin release, whereas a decrease from 1 to 0.3 or to 0.1 mM-Ca2+ lowered the release. These findings could reflect a relatively specific impairment in glucose handling by RINm5F cells, contrasting with the preserved response to other modulators of insulin release.