Two functional Na+/K(+)-ATPase isoforms in the left ventricle of guinea pig heart.
Guinea pig left ventricular muscle contains two distinct molecular forms of the Na+/K(+)-ATPase catalytic alpha subunit. Sarcolemmal vesicles highly enriched in Na+/K(+)-ATPase were isolated by a new procedure that yielded specific activities of 60-100 mumol Pi.h-1.mg-1. SDS/PAGE of isolated sarcolemma after reduction and alkylation of the sulfhydryl groups and identification on immunoblots with specific anti-(alpha subunit) antibodies indicated the presence of two major polypeptides of 100 kDa and 103 kDa, respectively. The two alpha subunits were functional: the dose/response curves of Na+/K(+)-ATPase activity with ouabain, dihydroouabain and digitoxigenin were biphasic, revealing the presence of high-affinity [concentration of drug causing 50% inhibition (IC50) = 10 nM] and low-affinity (IC50 = 2 microM) forms with proportional contributions of 55% and 45%, respectively. The involvement of the high-affinity form in the positive inotropic effect of digitalis and of the low-affinity sites in both inotropy and toxicity are consistent with the literature data on rodents.
Berrebi-Bertrand
I
I
Laboratoire de Pharmacologie des Transports Ioniques Membranaires, Université Paris VII, France.
Maixent
J M
JM
Guede
F G
FG
Gerbi
A
A
Charlemagne
D
D
Lelievre
L G
LG
D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D006168:Guinea Pigs; D007527:Isoenzymes / Q000302:isolation & purification*; D009206:Myocardium / Q000201:enzymology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis / Q000276:immunology / Q000302:isolation & purification*
D007527:Isoenzymes; D000254:Sodium-Potassium-Exchanging ATPase