[3H]Ouabain binding and Na+, K+-ATPase in resealed human red cell ghosts.

Abstract

The interaction of the cardiac glycoside [3H]ouabain with the Na+,K+ pump of resealed human erythrocyte ghosts was investigated . Binding of [3H]ouabain to high intracellular Na' ghosts was studied in high extracellular Na' media, a condition determined to produce maximal ouabain binding rates. Simultaneous examination of both the number of ouabain molecules bound per ghost and the corresponding inhibition of the Na +,K+-ATPase revealed that one molecule of [3H]ouabain inhibited one Na +,K+-ATPase complex. Intracellular magnesium or magnesium plus inorganic phosphate produced the lowest ouabain binding rate . Support of ouabain binding by adenosine diphosphate (ADP) was negligible, provided synthesis of adenosine triphosphate (ATP) through the residual adenylate kinase activity was prevented by the adenylate kinase inhibitor Ap5A . Uridine 5'-triphosphate (UTP) alone did not support ouabain binding after inhibition of the endogenous nucleoside diphosphokinase by trypan blue and depletion of residual ATP by the incorporation of hexokinase and glucose. ATP acting solely at the high-affinity binding site of the Na+,K+ pump (K m -1 jLM) promoted maximal [3H]ouabain binding rates. Failure of 5'-adenylyl-,8-y-imidophosphate (AMP-PNP) to stimulate significantly the rate of ouabain binding suggests that phosphorylation of the pump was required to expose the ouabain receptor .

Erythrocyte membrane lateral sterol domains: A dehydroergosterol fluorescence polarization study

“…Erythrocyte Ghosts Preparation. The method of ghost preparation was a modification of that of Shoemaker and Lauf (1983). Unsealed ghosts were prepared for sterolexchange assays, but the procedures employed were designed to be comparable to those required for preparation of sealed ghosts to simplify comparisons to other studies.…”