Calcium-sensing Receptor Activation Increases Cell-cell Adhesion and -cell Function

Abstract

Background/Aims: The extracellular calcium-sensing receptor (﴾CaR)﴿ is expressed in pancreatic -cells where it is thought to facilitate cell-to-cell communication and augment insulin secretion. However, it is unknown how CaR activation improves -cell function. Methods: Immunocytochemistry and western blotting confirmed the expression of CaR in MIN6 -cell line. The calcimimetic R568 (﴾1μM)﴿ 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 basalto- peak amplitude of ATP (﴾50μM)﴿ and tolbutamide (﴾100μM)﴿-evoked changes in cytosolic calcium. Activation of the receptor also increased PD98059 (﴾1-100μM)﴿ and SU1498 (﴾1-100μM)﴿- dependent -cell proliferation. Conclusion: Our data suggest that activation of the CaR increases E-cadherin mediated functional tethering between -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.