Okadaic acid and calyculin A inhibit agonist-stimulated calcium signaling and Ins(1,4,5)P3 production in rat hepatocytes, suggesting regulation by protein phosphorylation.
Hypothesis-generating for phosphatase control of hepatocyte calcium signaling; leaves open in vivo or disease relevance.
OKA2 and CL-A significantly inhibit the ability of angiotensin II, ATP and vasopressin to raise [Ca2+]i in rat hepatocytes, with a partial inhibition of the initial spike, and a complete inhibition of the following plateau. In contrast, the [Ca2+]i response to thapsigargin, which releases intracellular calcium stores through a mechanism independent of inositol phosphates, is much less affected. The ability of angiotensin II to stimulate Ins(1,4,5)P3 production is also reduced by OKA, with kinetics consistent with the inhibited [Ca2+]i response. Since OKA and CL-A are potent and selective inhibitors of phosphoprotein phosphatases, these results provide further evidence that agonist-stimulated Ins(1,4,5)P3 signalling can be inhibited by protein phosphorylation.
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Mattingly et al. (1992) studied this question.
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