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Phosphatidylinositol-4,5-bisphosphate (PIP2) is a membrane phosphoinositide that regulates the activity of many ion channels. Influx of calcium primarily through voltage-gated calcium (CaV) channels promotes insulin secretion in pancreatic β-cells. However, whether CaV channels are regulated by PIP2, as is the case for some non-insulin-secreting cells, is unknown. The purpose of this study was to investigate whether CaV channels are regulated by PIP2 depletion in pancreatic β-cells through activation of a muscarinic pathway induced by oxotremorine methiodide (Oxo-M). CaV channel currents were recorded by the patchclamp technique. The CaV current amplitude was reduced by activation of the muscarinic receptor 1 (M1R) in the absence of kinetic changes. The Oxo-M-induced inhibition exhibited the hallmarks of voltage-independent regulation and did not involve PKC activation. A small fraction of the Oxo-M-induced CaV inhibition was diminished by a high concentration of Ca2+ chelator, whereas ≽50% of this inhibition was prevented by diC8-PIP2 dialysis. Localization of PIP2 in the plasma membrane was examined by transfecting INS-1 cells with PH-PLCδ1, which revealed a close temporal association between PIP2 hydrolysis and CaV channel inhibition. Furthermore, the depletion of PIP2 by a voltage-sensitive phosphatase reduced CaV currents in a way similar to that observed following M1R activation. These results indicate that activation of the M1R pathway inhibits the CaV channel via PIP2 depletion by a Ca2+-dependent mechanism in pancreatic β- and INS-1 cells and thereby support the hypothesis that membrane phospholipids regulate ion channel activity by interacting with ion channels. [ABSTRACT FROM AUTHOR]

Phosphatidylinositol-4,5-bisphosphate (PIP 2 ) is a membrane phosphoinositide that regulates the activity of many ion channels. Influx of calcium primarily through voltage-gated calcium (Ca V ) channels promotes insulin secretion in pancreatic β-cells. However, whether Ca V channels are regulated by PIP 2 , as is the case for some non-insulin-secreting cells, is unknown. The purpose of this study was to investigate whether Ca V channels are regulated by PIP 2 depletion in pancreatic β-cells through activation of a muscarinic pathway induced by oxotremorine methiodide (Oxo-M). Ca V channel currents were recorded by the patch-clamp technique. The Ca V current amplitude was reduced by activation of the muscarinic receptor 1 (M 1 R) in the absence of kinetic changes. The Oxo-M-induced inhibition exhibited the hallmarks of voltage-independent regulation and did not involve PKC activation. A small fraction of the Oxo-M-induced Ca V inhibition was diminished by a high concentration of Ca 2+ chelator, whereas ≥50% of this inhibition was prevented by diC8-PIP 2 dialysis. Localization of PIP 2 in the plasma membrane was examined by transfecting INS-1 cells with PH-PLCδ1, which revealed a close temporal association between PIP 2 hydrolysis and Ca V channel inhibition. Furthermore, the depletion of PIP 2 by a voltage-sensitive phosphatase reduced Ca V currents in a way similar to that observed following M 1 R activation. These results indicate that activation of the M 1 R pathway inhibits the Ca V channel via PIP 2 depletion by a Ca 2+ -dependent mechanism in pancreatic β- and INS-1 cells and thereby support the hypothesis that membrane phospholipids regulate ion channel activity by interacting with ion channels., (Copyright © 2016 the American Physiological Society.)