Intravesicular pH changes in submitochondrial particles induced by monovalent cations: relationship to the Na+/H+ and K+/H+ antiporters.
The fluorescence of internalized fluorescein isothiocyanate dextran has been used to monitor the intravesicular pH of submitochondrial particles (SMP). Respiring SMP maintain a steady-state delta pH (interior acid) that results from the inwardly directed H+ flux of respiration and an opposing passive H+ leak. Addition of K+, Na+, or Li+ to SMP results in a shift to a more alkaline interior pH (pHi) in both respiring and nonrespiring SMP. The K+-dependent change in pHi, like the K+/H+ antiport in intact mitochondria, is inhibited by quinine and by dicyclohexylcarbodiimide. The Na+-dependent reaction is only partially inhibited by these reagents. Both the Na+- and the K+-dependent pH changes are sensitive to amiloride derivatives. The Km for both Na+ and K+ is near 20 mM whereas that for Li+ is closer to 10 mM. The K+/H+ exchange reaction is only slightly inhibited by added Mg2+, but abolished when A23187 is added with Mg2+. The passive exchange is optimal at pHi 6.5 with either Na+ or K+, and cannot be detected above pHi of 7.2. Both the Na+/H+ and the K+/H+ exchange reactions are optimal at an external pH of 7.8 in respiring SMP (pHi 7.1). Valinomycin stimulates the K+-dependent pH change in nonrespiring SMP, as does nigericin. It is concluded that SMP show K+/H+ antiport activity with properties distinct from those of Na+/H+ antiport. However, the properties of the K+/H+ exchange do not correspond in all respects to those of the antiport in intact mitochondria. Donnan equilibria and parallel uniport pathways for H+ and cations appear to contribute to cation-dependent pH changes in SMP.
Brierley
G P
GP
Department of Physiological Chemistry, Ohio State University Medical Center, Columbus 43210.
Davis
M H
MH
Jung
D W
DW
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002414:Cations, Monovalent / Q000494:pharmacology*; D002417:Cattle; D003911:Dextrans; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives*; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D008094:Lithium / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D008929:Mitochondria, Heart / Q000648:ultrastructure*; D011188:Potassium / Q000494:pharmacology; D027961:Potassium-Hydrogen Antiporters; D011803:Quinine / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers; D013050:Spectrometry, Fluorescence; D013367:Submitochondrial Particles / Q000378:metabolism*; D014634:Valinomycin / Q000494:pharmacology
D002352:Carrier Proteins; D002414:Cations, Monovalent; D003911:Dextrans; D005452:Fluoresceins; D005456:Fluorescent Dyes; D027961:Potassium-Hydrogen Antiporters; D017923:Sodium-Hydrogen Exchangers; C015219:fluorescein isothiocyanate dextran; D014634:Valinomycin; D000001:Calcimycin; D004024:Dicyclohexylcarbodiimide; D000584:Amiloride; D008094:Lithium; D012964:Sodium; D011803:Quinine; D016650:Fluorescein-5-isothiocyanate; D008274:Magnesium; D011188:Potassium; D002118:Calcium