OBJECTIVE: The presence of both alpha1- and alpha2-isoforms of the Na+/K+-ATPase (NKA) in cardiomyocytes indicates different functions. We hypothesized that preferential localization of the alpha2-isoform to the t-tubules, locally controlling the Na+/Ca2+-exchanger (NCX), underlies a specific role in Ca2+ handling. METHODS: We studied NKA isoform distribution in isolated cardiomyocytes from Wistar rats using immunocytochemistry. NKA pump and NCX currents (I(pump) and I(NCX)) were measured in control and detubulated cardiomyocytes. Intracellular Na+ concentration [Na+]i was assessed with the fluorescent dye SBFI. RESULTS: The alpha2-isoform abundance was higher in the t-tubules than in the surface sarcolemma. We established that 0.3 microM ouabain specifically blocked the alpha2-isoform in isolated rat cardiomyocytes. This low concentration blocked 10.7+/-0.6% of I(pump) in control, but only 6.0+/-0.5% in detubulated cardiomyocytes. Moreover, measured and calculated alpha1-specific and alpha2-specific I(pump) in control (547+/-29 pA and 66 pA, respectively) and in detubulated cells (495+/-30 pA and 31 pA, respectively) showed that 53% of the alpha2-isoform, but only 9.5% of the alpha1-isoform, were localized to the t-tubules. Despite the small abundance of the alpha2-isoform (approximately 11% of total NKA), selective inhibition of this isoform induced a 40% increase in contractility in field stimulated cardiomyocytes, but no increase in global [Na+]i. However, inhibition of the alpha2-isoform increased I(NCX) indicating local subsarcolemmal accumulation of Na+ near NCX. CONCLUSIONS: The alpha2-isoform of the NKA is functionally coupled to the NCX and can regulate Ca2+ handling without changing global [Na+]i.
OBJECTIVE: The presence of both alpha1- and alpha2-isoforms of the Na+/K+-ATPase (NKA) in cardiomyocytes indicates different functions. We hypothesized that preferential localization of the alpha2-isoform to the t-tubules, locally controlling the Na+/Ca2+-exchanger (NCX), underlies a specific role in Ca2+ handling. METHODS: We studied NKA isoform distribution in isolated cardiomyocytes from Wistar rats using immunocytochemistry. NKA pump and NCX currents (I(pump) and I(NCX)) were measured in control and detubulated cardiomyocytes. Intracellular Na+ concentration [Na+]i was assessed with the fluorescent dye SBFI. RESULTS: The alpha2-isoform abundance was higher in the t-tubules than in the surface sarcolemma. We established that 0.3 microM ouabain specifically blocked the alpha2-isoform in isolated rat cardiomyocytes. This low concentration blocked 10.7+/-0.6% of I(pump) in control, but only 6.0+/-0.5% in detubulated cardiomyocytes. Moreover, measured and calculated alpha1-specific and alpha2-specific I(pump) in control (547+/-29 pA and 66 pA, respectively) and in detubulated cells (495+/-30 pA and 31 pA, respectively) showed that 53% of the alpha2-isoform, but only 9.5% of the alpha1-isoform, were localized to the t-tubules. Despite the small abundance of the alpha2-isoform (approximately 11% of total NKA), selective inhibition of this isoform induced a 40% increase in contractility in field stimulated cardiomyocytes, but no increase in global [Na+]i. However, inhibition of the alpha2-isoform increased I(NCX) indicating local subsarcolemmal accumulation of Na+ near NCX. CONCLUSIONS: The alpha2-isoform of the NKA is functionally coupled to the NCX and can regulate Ca2+ handling without changing global [Na+]i.
Authors: Mordecai P Blaustein; Ling Chen; John M Hamlyn; Frans H H Leenen; Jerry B Lingrel; W Gil Wier; Jin Zhang Journal: J Physiol Date: 2016-07-31 Impact factor: 5.182
Authors: Nabeel J Al Moamen; Vikram Prasad; Ilona Bodi; Marian L Miller; Michelle L Neiman; Valerie M Lasko; Seth L Alper; David F Wieczorek; John N Lorenz; Gary E Shull Journal: J Mol Cell Cardiol Date: 2010-11-04 Impact factor: 5.000
Authors: William E Louch; Karina Hougen; Halvor K Mørk; Fredrik Swift; Jan M Aronsen; Ivar Sjaastad; Henrik M Reims; Borghild Roald; Kristin B Andersson; Geir Christensen; Ole M Sejersted Journal: J Physiol Date: 2009-12-14 Impact factor: 5.182
Authors: JuFang Wang; Erhe Gao; Jianliang Song; Xue-Qian Zhang; Jifen Li; Walter J Koch; Amy L Tucker; Kenneth D Philipson; Tung O Chan; Arthur M Feldman; Joseph Y Cheung Journal: Am J Physiol Heart Circ Physiol Date: 2009-12-11 Impact factor: 4.733