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.
%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
}