Role of caveolae in signal-transducing function of cardiac Na+/K+-ATPase

• Published in: American Journal of Physiology: Cell Physiology 2003-06, Vol.284 (6), p.C1550-C1560
• Main Authors: Liu, Lijun, Mohammadi, Kamiar, Aynafshar, Behrouz, Wang, Haojie, Li, Daxiang, Liu, Jiang, Ivanov, Alexander V, Xie, Zijian, Askari, Amir
• Format: Article
• Language: English
• Subjects: Animals; Animals, Newborn; Caveolae - chemistry; Caveolae - metabolism; Caveolin 1; Caveolin 3; Caveolins - metabolism; Cell Fractionation; Cells, Cultured; Enzyme Inhibitors - metabolism; Humans; In Vitro Techniques; Mitogen-Activated Protein Kinases - metabolism; Myocardial Contraction; Myocytes, Cardiac - cytology; Myocytes, Cardiac - metabolism; Ouabain - metabolism; Protein Subunits - isolation & purification; Protein Subunits - metabolism; Rats; Receptor, Epidermal Growth Factor - metabolism; Signal Transduction - physiology; Sodium-Potassium-Exchanging ATPase - metabolism; src-Family Kinases - metabolism; Swine
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.00555.2002

Departments of Pharmacology and Medicine, Medical College of Ohio, Toledo, Ohio 43614 Ouabain binding to Na + /K + -ATPase activates Src/epidermal growth factor receptor (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 intracellular Ca 2+ concentration ([Ca 2+ ] i ) and contractility. The goal of this study 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 1 - and 2 -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 -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 1 ) no change in total caveolar ERK1/2, but a two- to threefold increase in caveolar phosphorylated/activated ERK1/2; 2 ) no change in caveolar 1 -isoform and caveolin-3; and 3 ) 50-60% increases in caveolar Src and 2 -isoform. These findings, in conjunction with previous observations, show that components of the pathways that link Na + /K + -ATPase to ERK1/2 and [Ca 2+ ] i are organized within cardiac caveolae microdomains. They also suggest that ouabain-induced recruitments of Src and 2 -isoform to caveolae are involved in the manifestation of the positive inotropic effect of ouabain. digitalis; heart failure; rafts; sodium pump; Na + /Ca 2+ exchanger * L. Liu and K. Mohammadi contributed equally to this work.