Hepatic insulin effects independent of changes in Ca++ metabolism |
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Authors: | N Venkatesan M B Davidson |
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Affiliation: | Department of Medicine, Cedars-Sinai Medical Center and UCLA School of Medicine Room 516, Schuman Building, P.O. Box 48750 Los Angeles, California 90048, USA |
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Abstract: | The possibility of Ca++ acting as second messenger for insulin in rat liver was investigated using the net stimulation of 14C-glucose incorporation into glycogen by isolated hepatocytes as an index of insulin action. An insulin effect could be partially sustained in the virtual absence of Ca++ and Mg++ and a maximal insulin effect could be observed in the presence of either Ca++ or Mg++, suggesting that extracellular Ca++ is not required for insulin action. Inhibiting the activity of calmodulin, an intracellular mediator of Ca++ action, with trifluoperazine had little effect on insulin action. The efflux of 45Ca from prelabeled hepatocytes was not altered by the presence of insulin arguing against insulin-induced changes in Ca++ fluxes. Collectively, these results do not support the role of Ca++ as second messenger for insulin action in liver. |
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