Abstract
Tissue-distinct interactions of the Na(+)-K(+)-ATPase with Na(+) and K(+), independent of isoform-specific properties, were reported previously (A. G. Therien, N. B. Nestor, W. J. Ball, and R. Blostein. J. Biol. Chem. 271: 7104-7112, 1996). In this paper, we describe a detailed analysis of tissue-specific kinetics particularly relevant to regulation of pump activity by intracellular K(+), namely K(+) inhibition at cytoplasmic Na(+) sites. Our results show that the order of susceptibilities of alpha(1) pumps of various rat tissues to K(+)/Na(+) antagonism, represented by the ratio of the apparent affinity for Na(+) binding at cytoplasmic activation sites in the absence of K(+) to the affinity constant for K(+) as a competitive inhibitor of Na(+) binding at cytoplasmic sites, is red blood cell < axolemma approximately rat alpha(1)-transfected HeLa cells < small intestine < kidney < heart. In addition, we have carried out an extensive analysis of the kinetics of K(+) binding and occlusion to the cytoplasmic cation binding site and find that, for most tissues, there is a relationship between the rate of K(+) binding/occlusion and the apparent affinity for K(+) as a competitive inhibitor of Na(+) activation, the order for both parameters being heart >/= kidney > small intestine approximately rat alpha(1)-transfected HeLa cells. The notion that modulations in cytoplasmic K(+)/Na(+) antagonism are a potential mode of pump regulation is underscored by evidence of its reversibility. Thus the relatively high K(+)/Na(+) antagonism characteristic of kidney pumps was reduced when rat kidney microsomal membranes were fused into the dog red blood cell.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.