Role of caveolae in signal transducing function of cardiac Na+/K+-ATPase.
Liu, Lijun, Kamiar Mohammadi, Behrouz Aynafshar, Haojie Wang, Daxiang Li, Jiang Liu, Alexander V. Ivanov, Zijian Xie, and Amir Askari.
Departments of Pharmacology and Medicine, Medical College of Ohio, Toledo, Ohio 43614
APStracts 10:0062C, 2003.
Ouabain binding to Na+-K+-ATPase activates Src/EGFR to initiate multiple signal pathways that regulate growth. In cardiac myocytes and the intact heart, the early ouabain-induced pathways that cause rapid activations of ERK1/2 also regulate [Ca2+]i and contractility. The aim of this work was to explore the role of caveolae in these early signaling events. Subunits of Na+-K+-ATPase were detected by immunoblot analysis in caveolae isolated from cardiac myocytes, cardiac ventricles, kidney cell lines, and kidney outer medulla by established detergent-free procedures. Isolated rat cardiac caveolae contained Src, EGFR, ERK1/2, and 20-30% of cellular contents of a1 and a2 isoforms of Na+-K+-ATPase, along with nearly all of cellular caveolin-3. Immunofluorescence microscopy of adult cardiac myocytes showed the presence of caveolin-3 and a isoforms in peripheral sarcolemma and T tubules, and suggested their partial colocalization. Exposure of contracting isolated rat hearts to a positive inotropic dose of ouabain, and analysis of isolated cardiac caveolae showed that ouabain caused (a) no change in total caveolar ERK1/2, but two- to threefold increase in caveolar phosphorylated/activated ERK1/2; (b) no change in caveolar a1 isoform and caveolin-3; and (c) 50-60% increases in caveolar Src and a2 isoform. These findings, in conjunction with previous observations, show that components of the pathways that link Na+-K+-ATPase to ERK1/2 and [Ca2+]i are organized within cardiac caveolae microdomains. They also suggest that ouabain-induced recruitments of Src and a2 isoform to caveolae are involved in the manifestation of the positive inotropic effect of ouabain.
Received 26 November 2002; accepted in final form 13 February 2003
APS Manuscript Number C555-2.
Article publication pending Am J Physiol Cell Physiol
ISSN 1080-4757 Copyright 2003 The American Physiological Society.
Published in APStracts on 25 March 2003