Dissociation and redistribution of Na+,K(+)-ATPase from its surface membrane actin cytoskeletal complex during cellular ATP depletion.

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Abstract
Establishment and maintenance of a polar distribution of Na+,K(+)-ATPase is essential for efficient Na+ reabsorption by proximal tubule cells and is dependent upon the formation of a metabolically stable, detergent-insoluble complex of Na+,K(+)-ATPase with the actin membrane cytoskeleton. The present studies show that cellular ATP depletion results in a rapid duration-dependent dissociation of Na+,K(+)-ATPase from the actin cytoskeleton and redistribution of Na+,K(+)-ATPase to the apical membrane. During ATP depletion, total cellular Na+,K(+)-ATPase activity was unaltered, but the Triton-X-100-insoluble fraction (cytoskeleton associated) of Na+,K(+)-ATPase activity decreased (P less than 0.01), with a corresponding increase in the detergent-soluble fraction of Na+,K(+)-ATPase (P less than 0.01). Indirect immunofluorescent studies of cells with depleted ATP revealed a redistribution of Na+,K(+)-ATPase from the basolateral membrane into the apical membrane and throughout the cytoplasm. ATP depletion also resulted in the redistribution of F-actin from a primarily cortical concentration to a perinuclear location. There was also a rapid, duration-dependent conversion of monomeric G-actin to F-actin starting during the first 5 min of ATP depletion. Taken together, these data suggest that ATP depletion causes profound alterations in cell polarity by inducing major changes in the actin cytoskeletal architecture.

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