Pump by Protein Kinases

In smooth muscle cells a phosphorylation of the PM Ca2+-pump protein has been clearly demonstrated only for PKC. The regulation of the PMCA ATPase by cGK does not require concomitant phosphorylation of the pump. Although a modulation by cAK of the PM Ca2+ pump of erythrocytes and cardiac cells has been reported, such an effect could not be demonstrated for the ATPase from smooth muscle (see the following). 

The PM Ca2+ pump of smooth muscle may be preferentially fueled by ATP produced by a membrane-associated glycolytic system (Hardin et al, 1992). 

When endogenous glycolysis was the sole source of ATP, phosphorylation of the membranes by endogenous protein kinase activity induced a stimulation of the Ca2+ uptake that was more pronounced (up to three-fold stimulation) than in the presence of exogenously added ATP (Hardin etal., 1993). The characterization of these endogenous kinases is required for further evaluation of these results. 

Regulation of the Plasmalemmal Ca + Pump by Cyclic Nucleotide-Dependent Protein Kinases 

5-trisphosphate (IP3) receptor-like protein (Koga et al, 1994). A similar protein has been colocalized with the PM Ca2+-ATPase in caveolae (see Section IV. C). As yet, the mechanism of the regulation of the PM Ca + pump by cGK remains unresolved. 

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