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J. Biol. Chem., Vol. 276, Issue 10, 7136-7142, March 9, 2001

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Cytosolic Phospholipase A₂ Is Required for Optimal ATP Activation of BK Channels in GH₃ Cells^*

Donald D. Denson^§¶, Xiaoping Wang^§, Roger T. Worrell^§, Otor AlKhalili^§, and Douglas C. Eaton^§

From the Departments of  Anesthesiology and  Physiology and the ^§ Center for Cellular and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia 30322

To test the hypothesis that ATP activation of BK channels in GH₃ cells involves cytosolic phospholipase A₂ (cPLA₂) as a potential protein target for phosphorylation, we first inhibited the activity of cPLA₂ by both pharmacologic and molecular biologic approaches. Both approaches resulted in a decrease rather than an increase in BK channel activity by ATP, suggesting that in the absence of cPLA₂, phosphorylation of other regulatory elements, possibly the BK channel protein itself, results in inactivation rather than activation of the channel. The absence of changes in activity in the presence of the non-substrate ATP analog 5'-adenylyl-,-imidodiphosphate verified that ATP hydrolysis was required for channel activation by ATP. Experiments with an activator and inhibitor of protein kinase C (PKC) support the hypothesis that PKC can be involved in the activation of BK channels by ATP; and in the absence of PKC, other kinases appear to phosphorylate additional elements in the regulatory pathway that reduce channel activity. Our data point to cPLA₂- (but not cPLA₂-) as one target protein for phosphorylation that is intimately associated with the BK channel protein.

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