Novel regulation of Na+, K+‐ATPase by Src tyrosine kinases in cortical neurons

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Abstract
The Na+, K+-ATPase or Na+, K+-pump plays a critical role in ion homeostasis and many cellular events. The Na+, K+-pump activity is regulated by serine/threonine phosphorylation, the role of tyrosine kinases in the regulation, however, is obscure. We now present novel evidence showing that tyrosine phosphorylation activates the Na+, K+-pump in cortical neurons. The electrogenic activity of the Na+, K+-pump was measured using whole-cell voltage clamp. A tonic activity was revealed by an inward current induced by the specific inhibitor ouabain or strophanthidin; an outward current due to activation of the pump was triggered by raising extracellular K+. The inward and outward currents were attenuated by the tyrosine kinase inhibitor genistein, herbimycin A, or lavendustin A, while blocking tyrosine phosphatases increased the pump current. Down-regulation of the pump current was also seen with the Src inhibitor PP1 and intracellularly applied anti-Lyn or anti-Yes antibody. Consistently, intracellular application of Lyn kinase up-regulated the pump current. Immunoprecipitation and western blotting showed tyrosine phosphorylation and a direct interaction between Lyn and the alpha3 subunit of the Na+, K+-pump. The tyrosine phosphorylation of the alpha3 subunit was reduced by serum deprivation. These data suggest that the Na+, K+-ATPase activity in central neurons is regulated by specific Src tyrosine kinases via a protein-protein mechanism and may play a role in apoptosis.