The Na$^+$/K$^+$-ATPase (NKA) is the main route for Na$^+$
extrusion from cardiac myocytes. Different NKA alpha-subunit isoforms
are present in the heart. NKA-alpha1 is predominant, although there
is a variable amount of NKA-alpha2 in adult ventricular myocytes
of most species. It has been proposed that NKA-alpha2 is localized
mainly in T-tubules (TT), where it could regulate local Na$^+$/Ca$^2+$
exchange and thus cardiac myocyte Ca$^2+$. However, there is
controversy as to where NKA-alpha1 vs. NKA-alpha2 are localized in
ventricular myocytes. Here, we assess the TT vs. external sarcolemma
(ESL) distribution functionally using formamide-induced detubulation
of rat ventricular myocytes, NKA current (I(Pump)) measurements and
the different ouabain sensitivity of NKA-alpha1 (low) and NKA-alpha2
(high) in rat heart. Ouabain-dependent I(Pump) inhibition in control
myocytes indicates a high-affinity NKA isoform (NKA-alpha2, K(1/2)
= 0.38 +/- 0.16 microM) that accounts for 29.5 +/- 1.3\% of I(Pump)
and a low-affinity isoform (NKA-alpha1, K(1/2) = 141 +/- 17 microM)
that accounts for 70.5\% of I(Pump). Detubulation decreased cell
capacitance from 164 +/- 6 to 120 +/- 8 pF and reduced I(Pump) density
from 1.24 +/- 0.05 to 1.02 +/- 0.05 pA/pF, indicating that the functional
density of NKA is significantly higher in TT vs. ESL. In detubulated
myocytes, NKA-alpha2 accounted for only 18.2 +/- 1.1\% of I(Pump).
Thus, approximately 63\% of I(Pump) generated by NKA-alpha2 is from
the TT (although TT are only 27\% of the total sarcolemma), and the
NKA-alpha2/NKA-alpha1 ratio in TT is significantly higher than in
the ESL. The functional density of NKA-alpha2 is approximately 4.5
times higher in the T-tubules vs. ESL, whereas NKA-alpha1 is almost
uniformly distributed between the TT and ESL.
%0 Journal Article
%1 Desp_2007_321
%A Despa, Sanda
%A Bers, Donald M
%D 2007
%J Am. J. Physiol. Cell Physiol.
%K /&/ ATPase, Animals; Cardiac, Dose-Response Drug; Enzyme Factors Formamides, Heart Inhibitors, Isoenzymes, Membrane Myocytes, Ouabain, Potentials; Rats; Relationship, Sarcolemma, Sodium, Sodium-Potassium-Exchanging Time Ventricles, antagonists cytology/enzymology; drug effects/enzymology; inhibitors/metabolism; metabolism; pharmacology;
%N 1
%P C321--C327
%R 10.1152/ajpcell.00597.2006
%T Functional analysis of Na$^+$/K$^+$-ATPase isoform distribution
in rat ventricular myocytes.
%U http://dx.doi.org/10.1152/ajpcell.00597.2006
%V 293
%X The Na$^+$/K$^+$-ATPase (NKA) is the main route for Na$^+$
extrusion from cardiac myocytes. Different NKA alpha-subunit isoforms
are present in the heart. NKA-alpha1 is predominant, although there
is a variable amount of NKA-alpha2 in adult ventricular myocytes
of most species. It has been proposed that NKA-alpha2 is localized
mainly in T-tubules (TT), where it could regulate local Na$^+$/Ca$^2+$
exchange and thus cardiac myocyte Ca$^2+$. However, there is
controversy as to where NKA-alpha1 vs. NKA-alpha2 are localized in
ventricular myocytes. Here, we assess the TT vs. external sarcolemma
(ESL) distribution functionally using formamide-induced detubulation
of rat ventricular myocytes, NKA current (I(Pump)) measurements and
the different ouabain sensitivity of NKA-alpha1 (low) and NKA-alpha2
(high) in rat heart. Ouabain-dependent I(Pump) inhibition in control
myocytes indicates a high-affinity NKA isoform (NKA-alpha2, K(1/2)
= 0.38 +/- 0.16 microM) that accounts for 29.5 +/- 1.3\% of I(Pump)
and a low-affinity isoform (NKA-alpha1, K(1/2) = 141 +/- 17 microM)
that accounts for 70.5\% of I(Pump). Detubulation decreased cell
capacitance from 164 +/- 6 to 120 +/- 8 pF and reduced I(Pump) density
from 1.24 +/- 0.05 to 1.02 +/- 0.05 pA/pF, indicating that the functional
density of NKA is significantly higher in TT vs. ESL. In detubulated
myocytes, NKA-alpha2 accounted for only 18.2 +/- 1.1\% of I(Pump).
Thus, approximately 63\% of I(Pump) generated by NKA-alpha2 is from
the TT (although TT are only 27\% of the total sarcolemma), and the
NKA-alpha2/NKA-alpha1 ratio in TT is significantly higher than in
the ESL. The functional density of NKA-alpha2 is approximately 4.5
times higher in the T-tubules vs. ESL, whereas NKA-alpha1 is almost
uniformly distributed between the TT and ESL.
@article{Desp_2007_321,
abstract = {The {N}a$^{+}$/{K}$^{+}$-ATPase (NKA) is the main route for {N}a$^{+}$
extrusion from cardiac myocytes. Different NKA alpha-subunit isoforms
are present in the heart. NKA-alpha1 is predominant, although there
is a variable amount of NKA-alpha2 in adult ventricular myocytes
of most species. It has been proposed that NKA-alpha2 is localized
mainly in T-tubules (TT), where it could regulate local {N}a$^{+}$/{C}a$^{2+}$
exchange and thus cardiac myocyte {C}a$^{2+}$. However, there is
controversy as to where NKA-alpha1 vs. NKA-alpha2 are localized in
ventricular myocytes. Here, we assess the TT vs. external sarcolemma
(ESL) distribution functionally using formamide-induced detubulation
of rat ventricular myocytes, NKA current (I(Pump)) measurements and
the different ouabain sensitivity of NKA-alpha1 (low) and NKA-alpha2
(high) in rat heart. Ouabain-dependent I(Pump) inhibition in control
myocytes indicates a high-affinity NKA isoform (NKA-alpha2, K(1/2)
= 0.38 +/- 0.16 microM) that accounts for 29.5 +/- 1.3\% of I(Pump)
and a low-affinity isoform (NKA-alpha1, K(1/2) = 141 +/- 17 microM)
that accounts for 70.5\% of I(Pump). Detubulation decreased cell
capacitance from 164 +/- 6 to 120 +/- 8 pF and reduced I(Pump) density
from 1.24 +/- 0.05 to 1.02 +/- 0.05 pA/pF, indicating that the functional
density of NKA is significantly higher in TT vs. ESL. In detubulated
myocytes, NKA-alpha2 accounted for only 18.2 +/- 1.1\% of I(Pump).
Thus, approximately 63\% of I(Pump) generated by NKA-alpha2 is from
the TT (although TT are only 27\% of the total sarcolemma), and the
NKA-alpha2/NKA-alpha1 ratio in TT is significantly higher than in
the ESL. The functional density of NKA-alpha2 is approximately 4.5
times higher in the T-tubules vs. ESL, whereas NKA-alpha1 is almost
uniformly distributed between the TT and ESL.},
added-at = {2009-06-03T11:20:58.000+0200},
author = {Despa, Sanda and Bers, Donald M},
biburl = {https://www.bibsonomy.org/bibtex/2ab05764408065e802391d90fadc786f3/hake},
description = {The whole bibliography file I use.},
doi = {10.1152/ajpcell.00597.2006},
file = {Desp_2007_321.pdf:Desp_2007_321.pdf:PDF},
institution = {Dept. of Physiology, Loyola University Chicago, Stritch School of
Medicine, 2160 South First Ave., Maywood, IL 60153, USA.},
interhash = {772b8f649bd1b5d3d59f29e21632a9d8},
intrahash = {ab05764408065e802391d90fadc786f3},
journal = {Am. J. Physiol. Cell Physiol.},
keywords = {/&/ ATPase, Animals; Cardiac, Dose-Response Drug; Enzyme Factors Formamides, Heart Inhibitors, Isoenzymes, Membrane Myocytes, Ouabain, Potentials; Rats; Relationship, Sarcolemma, Sodium, Sodium-Potassium-Exchanging Time Ventricles, antagonists cytology/enzymology; drug effects/enzymology; inhibitors/metabolism; metabolism; pharmacology;},
month = Jul,
number = 1,
pages = {C321--C327},
pdf = {Desp_2007_321.pdf},
pii = {00597.2006},
pmid = {17392375},
timestamp = {2009-06-03T11:21:09.000+0200},
title = {Functional analysis of {N}a$^{+}$/{K}$^{+}$-ATPase isoform distribution
in rat ventricular myocytes.},
url = {http://dx.doi.org/10.1152/ajpcell.00597.2006},
volume = 293,
year = 2007
}