Characterization of the mitochondrial Na+H+ exchange. The effect of amiloride analogues

András Kapus, Gergely L. Lukács, Edward J. Cragoe, Erzsébet Ligeti, Attila Fonyó

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Abstract

The kinetic properties and inhibitor sensitivity of the Na+H+ exchange activity present in the inner membrane of rat heart and liver mitochondria were studied. (1) Na+-induced H+ efflux from mitochondria followed Michaelis-Menten kinetics. In heart mitochondria, the Km for Na+ was 24 ± 4 mM and the Vmax was 4.5 ± 1.4 nmol H+/mg protein per s (n = 6). Basically similar values were obtained in liver mitochondria (Km = 31 ± 2 mM, Vmax = 5.3 ± 0.2 nmol H+/mg protein per s, n = 4). (2) Li+ proved to be a substrate (Km = 5.9 mM, Vmax = 2.3 nmol H+/mg protein per s) and a potent competitive inhibitor with respect to Na+ (Ki ≈ 0.7 mM). (3) External H+ inhibited the mitochondrial Na+H+ exchange competitively. (4) Two benzamil derivatives of amiloride, 5-(N-4-chlorobenzyl)-N-(2′,4′-dimethyl)benzamil and 3′,5′-bis(trifluoromethyl)benzamil were efective inhibitors of the mitochondrial Na+H+ exchange (50% inhibition was attained by approx. 60 μM in the presence of 15 mM Na+). (5) Three 5- amino analogues of amiloride, which are very strong Na+H+ exchange blockers on the plasma membrane, exerted only weak inhibitory activity on the mitochondrial Na+H+ exchange. (6) The results indicate that the mitochondrial and the plasma membrane antiporters represent distinct molecular entities.

Original languageEnglish
Pages (from-to)383-390
Number of pages8
JournalBBA - Biomembranes
Volume944
Issue number3
DOIs
Publication statusPublished - Oct 20 1988

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Keywords

  • (Rat liver and heart)
  • Amiloride analogue
  • Mitochondrial inner membrane
  • Plasma membrane
  • Sodium ion-proton exchange

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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