Relative abundance of alpha2 Na(+) pump isoform influences Na(+)-Ca(2+) exchanger currents and Ca(2+) transients in mouse ventricular myocytes.
In the mouse, genetic reduction in the Na(+), K(+)-ATPase alpha1 or alpha2 isoforms results in different functional phenotypes: heterozygous alpha2 isolated hearts are hypercontractile, whereas heterozygous alpha1 hearts are hypocontractile. We examined Na(+)/Ca(2+) exchange (NCX) currents in voltage clamped myocytes (pipette [Na(+)]=15 mM) induced by abrupt removal of extracellular Na(+). In wild-type (WT) myocytes, peak exchanger currents were 0.59+/-0.04 pA/pF (mean+/-S.E.M., n=10). In alpha1(+/-) myocytes (alpha2 isoform increased by 54%), NCX current was reduced to 0.33+/-0.05 (n=9, P<0.001) indicating a lower subsarcolemmal [Na(+)]. In alpha2(+/-) myocytes (alpha2 isoform reduced by 54%), the NCX current was increased to 0.89+/-0.11 (n=8, P=0.03). The peak sarcolemmal Na(+) pump currents activated by abrupt increase in [K(+)](o) to 4 mM in voltage clamped myocytes in which the Na(+) pump had been completely inhibited for 5 min by exposure to 0 [K(+)](o) were similar in alpha1(+/-) (0.86+/-0.12, n=10) and alpha2(+/-) myocytes (0.94+/-0.08 pA/pF, n=16), and were slightly but insignificantly reduced relative to WT (1.03+/-0.05, n=24). The fluo-3 [Ca(2+)](i) transient (F/F(o)) in WT myocytes paced at 0.5 Hz was 2.18+/-0.09, n=34, was increased in alpha2(+/-) myocytes (F/F(o)=2.56+/-0.14, n=24, P=0.02), and was decreased in alpha1(+/-) myocytes (F/F(o)=1.93+/-0.08, n=28, P<0.05). Thus the alpha2 isoform rather than the alpha1 appears to influence Na(+)/Ca(2+) exchanger currents [Ca(2+)](i) transients, and contractility. This finding is consistent with the proposal that alpha2 isoform of the Na pump preferentially alters [Na(+)] in a subsarcolemmal micro-domain adjacent to Na(+)/Ca(2+) exchanger molecules and SR Ca(2+) release sites.
Yamamoto
Taku
T
Cardiology Division, University of Utah Health Sciences Center, 50 North Medical Drive, Salt Lake City, UT 84132, USA.
Su
Zhi
Z
Moseley
Amy E
AE
Kadono
Toshie
T
Zhang
John
J
Cougnon
Marc
M
Li
Fenghua
F
Lingrel
Jerry B
JB
Barry
William H
WH
D000818:Animals; D020013:Calcium Signaling; D002478:Cells, Cultured; D006352:Heart Ventricles / Q000166:cytology; D051379:Mice; D008822:Mice, Transgenic; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D012508:Sarcolemma / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000235:genetics / Q000378:metabolism*
D020033:Protein Isoforms; C491739:Slc8a2 protein, mouse; D019831:Sodium-Calcium Exchanger