L-histidine sensing by calcium sensing receptor inhibits voltage-dependent calcium channel activity and insulin secretion in β-cells

Aims: Our goal was to test the hypothesis that the histidine-induced activation of calcium sensing receptor (CaR) can regulate calcium channel activity of L-type voltage dependent calcium channel (VDCC) due to increased spatial interaction between CaR and VDCC in beta-cells and thus modulate glucose-induced insulin secretion. Main methods: Rat insulinoma (RINr1046-38) insulin-producing beta-cells were cultured in RPMI-1640 medium on 25 mm diameter glass coverslips in six-well culture plates in a 5% CO2 incubator at 37 degrees C. The intracellular calcium concentration, [Ca2+](i), was determined by ratio fluorescence microscopy using Fura-2AM. The spatial interactions between CaR and L-type VDCC in beta-cells were measured by immunofluorescence confocal microscopy using a Nikon C1 laser scanning confocal microscope. The insulin release was determined by enzyme-linked immunosorbent assay (ELISA). Key findings: The addition of increasing concentrations of L-histidine along with 10 mM glucose resulted in 57% decrease in [Ca2+](i). The confocal fluorescence imaging data showed 5.59 to 8.62-fold increase in colocalization correlation coefficient between CaR and VDCC in beta-cells exposed to L-histidine thereby indicating increased membrane delimited spatial interactions between these two membrane proteins. The insulin ELISA data showed 54% decrease in the 1st phase of glucose-induced insulin secretion in beta-cells exposed to increasing concentrations of L-histidine. Significance: L-histidine-induced increased spatial interaction of CaR with VDCC can inhibit calcium channel activity of VDCC and consequently regulate glucose-induced insulin secretion by beta-cells. The L-type VDCC could therefore be a potential therapeutic target in diabetes. (C) 2011 Elsevier Inc. All rights reserved.