Modulation of glucose-induced insulin secretion from a rat clonal beta-cell line

The present studies demonstrate that the beta-cell line RINr1046-38 (RIN-38) retains the capability to secrete insulin in response to glucose. The maximal effect of glucose was a 5- to 9-fold stimulation of insulin secretion from RIN-38 cells. This glucose-induced insulin secretion was maximal at 0.6 mM and was modulated by other secretagogues. Potassium concentrations of 10 mM, adenylate cyclase activators (glucagon-like peptide-1 and forskolin), and a phosphodiesterase inhibitor (isobutylmethylxanthine) potentiated glucose-induced insulin secretion, but had little or no effect on insulin secretion in the absence of glucose. Potassium concentrations of 20 mM or more, glibenclamide, and carbachol (Cch) stimulated insulin secretion 8- to 12-fold in the absence of glucose, while only Cch potentiated the effect of glucose on insulin secretion. Amino acids (alanine, arginine, leucine, and ketoisocaproate) also stimulated insulin secretion. The alpha 2-adrenergic agonist clonidine (1 microM), low extracellular calcium (less than or equal to 0.5 mM), and extended culture of RIN-38 cells at low glucose concentrations (0.33 mM) inhibited the stimulatory effect of glucose on insulin secretion. Insulin secretion was retained in RIN-38 cells for up to 98 passages. However, extended passage was associated with a decline in cellular insulin content (83% decline over 89 passages). In addition, high passage cells lost the ability to secrete insulin in response to glucose, but continued to respond to other secretagogues (K+, alanine, and carbachol). In fact, in the absence of glucose the effect of Cch on insulin secretion was well maintained in high passage cells (8- and 9.9-fold increase in insulin secretion, passages 9 and 70, respectively). Thus, low passage RIN-38 cells secrete insulin in response to glucose and other insulin secretagogues. High passage cells do not respond to glucose, but continue to respond to other secretagogues. Based on these results we propose that high and low passage RIN-38 cells provide a model for examining molecular mechanisms of glucose-induced insulin secretion. In addition, these findings emphasize that passage information is essential for interpretation of secretion studies with RIN cell lines.