Short-Term NO Synthase Inhibition and the Na+-Binding
Properties of Cardiac Na,K-ATPase
N. Vrbjar, M. Strnisková, O. Pecháňová1,
M. Gerová1
Institute for Heart Research, Slovak Academy of Sciences and
1Institute of Normal and Pathological Physiology, Slovak
Academy of Sciences, Bratislava, Slovak Republic
Received July
30, 1999
Accepted September 21, 1999
Summary
It is known that hypertension is accompanied by increased [Na+]i.
The functional properties of Na,K-ATPase, which transports the
Na+ out and K+ into myocardial cells during the relaxation
phase, were investigated in the left ventricle (LV), septum (SV)
and the right ventricle (RV) of anesthetized dogs with moderate
acute blood pressure elevation elicited by short-term (4-hour)
NO synthase inhibition. The NO-insufficiency was induced by
administration of an L-arginine analogue, the NG-nitro-L-arginine
methyl ester (L-NAME). Concerning the function of Na,K-ATPase
under the conditions of lowered NO synthesis, we focused our
attention to the binding of Na+ to the enzyme molecule.
Activation of the enzyme by increasing Na+ concentrations
revealed significant changes in both the maximal velocity (Vmax)
and the affinity for Na+ (KNa) in all investigated heart
sections. The Vmax increased by 27 % in LV, by 87 % in SV and by
58 % in RV. The KNa value increased by 86 % in LV, by 105 % in
SV and by 93% in RV, indicating an apparent decrease in the
sensitivity of the Na+-binding site in the Na,K-ATPase molecule.
This apparently decreased pump affinity for Na+ together with
the increase of Vmax suggest that, during the short-term
inhibition of NO synthesis, the Na,K-ATPase is capable of
extruding the excessive Na+ from the myocardial cells more
effectively at higher [Na+]i as compared to the Na,K-ATPase of
control animals.
Key
words
Na,K-ATPase · Heart · Pressure overload · Nitric oxide · L-NAME
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requests
Norbert Vrbjar, Institute for Heart Research, Slovak Academy of Sciences, Dúbravská
cesta 9, 842 33 Bratislava, Slovak Republic. E-mail: usrdnorb@savba.sk
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