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.
