Inhibition of Phosphatases and Increased Ca2+ Channel Activity by Inositol Hexakisphosphate

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Science  17 Oct 1997:
Vol. 278, Issue 5337, pp. 471-474
DOI: 10.1126/science.278.5337.471

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Inositol hexakisphosphate (InsP6), the dominant inositol phosphate in insulin-secreting pancreatic β cells, inhibited the serine-threonine protein phosphatases type 1, type 2A, and type 3 in a concentration-dependent manner. The activity of voltage-gated L-type calcium channels is increased in cells treated with inhibitors of serine-threonine protein phosphatases. Thus, the increased calcium channel activity obtained in the presence of InsP6 might result from the inhibition of phosphatase activity. Glucose elicited a transient increase in InsP6 concentration, which indicates that this inositol polyphosphate may modulate calcium influx over the plasma membrane and serve as a signal in the pancreatic β cell stimulus-secretion coupling.

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