Characterization of the mitochondrial Na+-H+ exchange. The effect of amiloride analogues.
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 approximately 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 effective inhibitors of the mitochondrial Na+-H+ exchange (50% inhibition was attained by approx. 60 microM 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.
Kapus
A
A
Department of Physiology, Semmelweis Medical University, Budapest, Hungary.
Lukács
G L
GL
Cragoe
E J
EJ
Ligeti
E
E
Fonyó
A
A
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology*; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D008929:Mitochondria, Heart / Q000187:drug effects* / Q000378:metabolism; D008930:Mitochondria, Liver / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D012964:Sodium