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  • Title: Exaprolol as a modulator of heart sarcolemmal (Na+ + K+)-ATPase. Evidence for interaction with an essential sulfhydryl group in the catalytic centre of the enzyme.
    Author: Dzurba A, Ziegelhöffer A, Schmidtová L, Breier A, Vrbjar N, Okolicány J.
    Journal: Gen Physiol Biophys; 1985 Jun; 4(3):257-64. PubMed ID: 2863195.
    Abstract:
    Beta-adrenoceptor blocking agents may have, in addition to their primary action, also ancillary effects on the cell membrane. In the present paper the non-specific interaction of exaprolol with the ATPase systems in isolated rat heart sarcolemmal membranes was investigated. When preincubated with sarcolemmal membranes in vitro, exaprolol in concentrations below 10(-4) mol.l-1 had no significant effect on sarcolemmal Mg2+-, Ca2+- and (Na+ + K+)-ATPase activities. At exaprolol concentration of 10(-4) mol.l-1 the Mg2+- and Ca2+-ATPase activities became inhibited whereas the (Na+ + K+)-ATPase activity was markedly stimulated. A kinetic analysis of these interactions revealed a non-competitive inhibition of Mg2+- and Ca2+-ATPase. In the case of (Na+ + K+)-ATPase a synergistic type of stimulation characterized by an exaprolol-induced conversion of an essential sulfhydryl group in the active site of the enzyme to the more reactive [S-] form has been observed thus increasing the affinity of the enzyme to ATP. Exaprolol concentrations exceeding 5 X 10(-4) mol.l-1 induced an overall depression of the investigated enzyme activities.
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