Na+/H+ exchange in mitochondria as monitored by BCECF fluorescence.
The recently developed method of loading isolated heart mitochondria with the fluorescent pH indicator, BCECF, was applied to monitor the Na+o/H+i exchange process from the matrix side of the membrane. The Na+-induced changes in the pH of the matrix (pHm) showed that: (i) the Na+o/H+i exchange followed Michaelis-Menten kinetics with respect to external Na+ with a Km of approx. 20 mM; (ii) in contrast to this, the dependence of the exchange rate on the matrix [H+] did not obey the Michaelian model. No Na+-induced alkalinization occurred above a pHm of 7.45 +/- 0.09 (n = 4). Below this value the reciprocal of the transport rate and that of the matrix [H+] deviated upwardly from the straight line. The results suggest that internal H+ might exert allosteric control on the mitochondrial Na+/H+ exchange process.
Kapus
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A
Department of Physiology, Semmelweis University of Medicine, Budapest, Hungary.
Ligeti
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E
Fonyó
A
A
D000818:Animals; D000968:Antimycin A / Q000494:pharmacology; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D008929:Mitochondria, Heart / Q000187:drug effects / Q000378:metabolism*; D011522:Protons; D051381:Rats; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers; D013050:Spectrometry, Fluorescence
D002352:Carrier Proteins; D005452:Fluoresceins; D005456:Fluorescent Dyes; D011522:Protons; D017923:Sodium-Hydrogen Exchangers; D000968:Antimycin A; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D012964:Sodium