Calcium-Sensing Receptor Activation Increases Cell-Cell Adhesion and β-Cell Function

Background/Aims: The extracellular calcium-sensing receptor (CaR) is expressed in pancreatic beta-cells where it is thought to facilitate cell-to-cell communication and augment insulin secretion. However, it is unknown how CaR activation improves beta-cell function. Methods: Immunocytochemistry and western blotting confirmed the expression of CaR in MIN6 beta-cell line. The calcimimetic R568 (1 mu M) was used to increase the affinity of the CaR and specifically activate the receptor at a physiologically appropriate extracellular calcium concentration. Incorporation of 5-bromo-2'-deoxyuridine (BrdU) was used to measure cell proliferation, whilst changes in non-nutrient-evoked cytosolic calcium were assessed using fura-2-microfluorimetry. AFM-single-cell-force spectroscopy related CaR-evoked changes in epithelial (E)-cadherin expression to improved functional tethering between coupled cells. Results: Activation of the CaR over 48hr doubled the expression of E-cadherin (206 +/- 41%) and increased L-type voltage-dependent calcium channel expression by 70% compared to control. These changes produced a 30% increase in cell-cell tethering and elevated the basal-to-peak amplitude of ATP (50 mu M) and tolbutamide (100 mu M)-evoked changes in cytosolic calcium. Activation of the receptor also increased PD98059 (1-100 mu M) and SU1498 (1-100 mu M)-dependent beta-cell proliferation. Conclusion: Our data suggest that activation of the CaR increases E-cadherin mediated functional tethering between beta-cells and increases expression of L-type VDCC and secretagogue-evoked changes in [Ca2+](i). These findings could explain how local changes in calcium, co-released with insulin, activate the CaR on neighbouring cells to help ensure efficient and appropriate secretory function. Copyright (c) 2012 S. Karger AG, Basel