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MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

Role of endosomal Na⁺-K⁺-ATPase and cardiac steroids in the regulation of endocytosis

¹The Kuvin Center for the Study of Infectious and Tropical Diseases, Institute of Microbiology, and ²Department of Physiology, The Hebrew University-Hadassah Medical School, Jerusalem, Israel

Submitted 5 December 2006 ; accepted in final form 5 June 2007

Plasma membrane Na⁺-K⁺-ATPase, which drives potassium into and sodium out of the cell, has important roles in numerous physiological processes. Cardiac steroids (CS), such as ouabain and bufalin, specifically interact with the pump and affect ionic homeostasis, signal transduction, and endocytosed membrane traffic. CS-like compounds are present in mammalian tissues, synthesized in the adrenal gland, and considered to be new family of steroid hormones. In this study, the mechanism of Na⁺-K⁺-ATPase involvement in the regulation of endocytosis is explored. We show that the effects of various CS on changes in endosomal pH are mediated by the pump and correspond to their effects on endosomal membrane traffic. In addition, it was found that CS-induced changes in endocytosed membrane traffic were dependent on alterations in [Na⁺] and [H⁺] in the endosome. Furthermore, we show that various CS differentially regulate endosomal pH and membrane traffic. The results suggest that these differences are due to specific binding characteristics. Based on our observations, we propose that Na⁺-K⁺-ATPase is a key player in the regulation of endosomal pH and endocytosed membrane traffic. Furthermore, our results raise the possibility that CS-like hormones regulate differentially intracellular membrane traffic.

bufalin; ouabain; endosomal pH

This article has been cited by other articles:

				A. Y. Bagrov, J. I. Shapiro, and O. V. Fedorova Endogenous Cardiotonic Steroids: Physiology, Pharmacology, and Novel Therapeutic Targets Pharmacol. Rev., March 1, 2009; 61(1): 9 - 38. [Abstract] [Full Text] [PDF]