Protein kinases A and C stimulate the Na+ active transport in frog skeletal muscle without an appreciable change in the number of sarcolemmal Na+ pumps.

AIM

The activation of both protein kinases A (PKA) and protein kinases C (PKC) in some cell types increases and in others reduces active Na+ efflux. These effects have been ascribed to either a change in the rate of ionic translocation by a fixed number of Na+ pumps or, a change in the number of plasma membrane pumps. The purpose of the present experiments was to study the effect of activating PKA and PKC on the Na+ extrusion by the Na+ pump in frog skeletal muscle.

METHODS

Na+ (22Na+) fluxes and ouabain (3H-ouabain) binding were measured in frog sartorius muscles.

RESULTS

Both activation of PKA and PKC increased the active Na+ extrusion by a factor of two; these effects were not additive. Ouabain binding experiments indicated that the pump stimulation by activation of these kinases is not associated with any significant increase in the number of plasma membrane pumps. Stimulation of the active Na+ efflux by protein kinase activation (no change in the number of sarcolemmal pumps) and by hypotonicity (increase in the number of pumps) could be elicited in the same preparation and they were additive.

CONCLUSION

It is concluded that in frog skeletal muscle fibres, (1) activation of both PKA and PKC stimulate the Na+ pump by increasing its rate of ionic translocation; and (2) two modes of Na+ active transport (with and without an increase in the number of pumps) are operative, and can be at work simultaneously, a phenomenon to be reckoned with.