Rapid turnover of phosphatidylinositol-4,5-bisphosphate in insulin-secreting cells mediated by Ca2+ and the ATP-to-ADP ratio

• Phosphatidylinositol-4,5-bisphosphate (PIP2) is important for a variety of cellular processes as a precursor for second messengers and by regulating ion channels, the cytoskeleton, and vesicle traffic in many types of cells, including insulin-secreting β-cells. Here, we applied evanescent wave microscopy and the PIP2-binding pleckstrin homology domain from phospholipase C (PLC)-δ fused to the green fluorescent protein to characterize the regulation of plasma membrane PIP2 in individual insulin-secreting MIN6 β-cells. Elevation of the glucose concentration from 3 to 11 mmol/l evoked antisynchronous oscillations of [PIP2] and cytoplasmic Ca2+concentration, consistent with PLC being periodically activated by the voltage-dependent Ca2+ influx. The effect of adenine nucleotides on [PIP2] was studied in cells permeabilized with α-toxin. ATP dose- dependently stimulated PIP2 synthesis with half-maximal effect at 300 μmol/l. Omission of the nucleotide resulted in rapid loss of PIP2 with t1/2 < 40 s. ADP also stimulated PIP2 formation, but this effect reflected local ATP formation and was prevented by the adenylate kinase inhibitor diadenosine-pentaphosphate. The ATP-induced PIP2 synthesis was counteracted by the ADP analog adenosine-5′-O-2-thiodiphosphate. We conclude that plasma membrane PIP2 is dynamically regulated by intracellular Ca2+ and the ATP-to-ADP ratio in insulin-secreting cells. The rapid turnover allows maintenance of PIP2 levels while generating second messengers of critical importance for insulin secretion.

Nyckelord

Adenosine Diphosphate/*metabolism

Adenosine Triphosphate/*metabolism

Animals

Calcium/*metabolism

Cell Line

Cell Membrane/metabolism

Glucose

Hydrolysis

Insulin-Secreting Cells/*metabolism

Mice

Phosphatidylinositol 4;5-Diphosphate/*metabolism

MEDICINE

MEDICIN

Publikations- och innehållstyp

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