%0 Journal Article %1 Swif_2007_109 %A Swift, Fredrik %A Tovsrud, Nils %A Enger, Ulla H %A Sjaastad, Ivar %A Sejersted, Ole M %D 2007 %J Cardiovasc. Res. %K /&/ ATPase, Animals; Blotting, Calcium, Cardiac, Cell Confocal; Contraction, Electric Exchanger, Immunohistochemistry; Male; Microscopy, Myocardial Myocytes, Ouabain, Patch-Clamp Rats, Rats; Size; Sodium, Sodium-Calcium Sodium-Potassium-Exchanging Stimulation; Techniques; Western, Wistar; analysis/antagonists analysis/metabolism; enzymology/physiology; inhibitors/metabolism metabolism; methods; pharmacology; physiology; %N 1 %P 109--117 %R 10.1016/j.cardiores.2007.03.017 %T The Na$^+$/K$^+$-ATPase alpha2-isoform regulates cardiac contractility in rat cardiomyocytes. %U http://dx.doi.org/10.1016/j.cardiores.2007.03.017 %V 75 %X 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$^+$/Ca$^2+$-exchanger (NCX), underlies a specific role in Ca$^2+$ 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 Ca$^2+$ handling without changing global Na$^+$i.

@article{Swif_2007_109, abstract = {OBJECTIVE: The presence of both alpha1- and alpha2-isoforms of the {N}a$^{+}$/{K}$^{+}$-ATPase (NKA) in cardiomyocytes indicates different functions. We hypothesized that preferential localization of the alpha2-isoform to the t-tubules, locally controlling the {N}a$^{+}$/{C}a$^{2+}$-exchanger (NCX), underlies a specific role in {C}a$^{2+}$ 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 {N}a$^{+}$ concentration [{N}a$^{+}$]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 [{N}a$^{+}$]i. However, inhibition of the alpha2-isoform increased I(NCX) indicating local subsarcolemmal accumulation of {N}a$^{+}$ near NCX. CONCLUSIONS: The alpha2-isoform of the NKA is functionally coupled to the NCX and can regulate {C}a$^{2+}$ handling without changing global [{N}a$^{+}$]i.}, added-at = {2009-06-03T11:20:58.000+0200}, author = {Swift, Fredrik and Tovsrud, Nils and Enger, Ulla H and Sjaastad, Ivar and Sejersted, Ole M}, biburl = {https://www.bibsonomy.org/bibtex/2ee8bb05db31999613d541e0cbb6cf828/hake}, description = {The whole bibliography file I use.}, doi = {10.1016/j.cardiores.2007.03.017}, file = {Swif_2007_109.pdf:Swif_2007_109.pdf:PDF}, institution = {Institute for Experimental Medical Research, Ullevaal University Hospital, University of Oslo, Oslo, Norway. fredrik.swift@medisin.uio.no}, interhash = {824405cc13475f9df99e2e3b542f25ff}, intrahash = {ee8bb05db31999613d541e0cbb6cf828}, journal = {Cardiovasc. Res.}, keywords = {/&/ ATPase, Animals; Blotting, Calcium, Cardiac, Cell Confocal; Contraction, Electric Exchanger, Immunohistochemistry; Male; Microscopy, Myocardial Myocytes, Ouabain, Patch-Clamp Rats, Rats; Size; Sodium, Sodium-Calcium Sodium-Potassium-Exchanging Stimulation; Techniques; Western, Wistar; analysis/antagonists analysis/metabolism; enzymology/physiology; inhibitors/metabolism metabolism; methods; pharmacology; physiology;}, month = Jul, number = 1, pages = {109--117}, pdf = {Swif_2007_109.pdf}, pii = {S0008-6363(07)00142-3}, pmid = {17442282}, timestamp = {2009-06-03T11:21:33.000+0200}, title = {The {N}a$^{+}$/{K}$^{+}$-ATPase alpha2-isoform regulates cardiac contractility in rat cardiomyocytes.}, url = {http://dx.doi.org/10.1016/j.cardiores.2007.03.017}, volume = 75, year = 2007 }