Translocation of some Anions Cations and Acids in Rat Liver Mitochondria

Abstract

Studies of net translocation of various anions and cations and their corresponding acids and bases, using extensions of established techniques, imply that the M phase of the cristae membrane of rat liver mitochondria is very impermeable (i. e. not permitting net permeation) to the following ions: CH,COO-, H,PO;, HPOi-, SO:-, Fe(CN)i-, Fe(CN):-, choline+, K+, Na+ and NH:. However, the M phase appears to be permeated rapidly by SCN-and slowly by C1-.It has been confirmed that CH3COO-and "Ha probably permeate as CH3COOH and NH, respectively, and that phosphate equilibrates across the M phase by an electrically neutral mechanism equivalent to H,PO, translocation. The possibility that phosphate is obligatorily translocated as KKPO, has been eliminated.Sulphate equilibrates by an electrically neutral mechanism equivalent to H,SO, translocation. The alkali metals Na+ and K+ (and possibly N H f ) equilibrate across the M phase via specific electrically neutral H+/Na+ and H+/K+ antiport, the former being the more active a t neutral pH. Choline does not participate significantly in proton-coupled antiport.When resting rat liver mitochondria are suspended in isotonic solutions of the ammonium salts of various acids, the net rate of entry of the salt, and the rate of swelling observed semi-quantitatively by the change of light-sca,ttering, have been found by Chappell and co-workers [ -141 to depend on the acid or anionic component of the salt. It has been assumed [4] that neither NH: ion nor the charged anion An-can permeate the membrane as such, but that NH, can dissolve in and pass through the hydrophobic osmotic barrier (M phase) of the cristae membrane, and that net entry of salt is therefore conditional on a process equivalent to the entry of the acid AH,, as illustrated by the following translocation equations in which curved arrows denote chemical reaction and straight arrows denote translocation : H20where the anion AH&l, is written as 4-for simplicity, and where the circle between the two straight arrows denotes direct coupling between the corresponding translocation reactions. However, taking into account the osmotic equilibration of H,O across the membrane, the net translocation reaction of equations ( 2 ) and ( Chappell [a] has drawn the conclusion that the cristae membrane is anion-and cation-impermeable in the usual (uniport) sense, but that certain anions, such as arsenate, phosphate and acetate equilibrate across the cristae membrane of rat liver mitochondria by non-electrogenic reactions corresponding to acid uniport as described by equations ( 2 ) or (3) (see [6] for nomenclature), whereas other anions, such as chloride or sulphate do not equilibrate by such reactions. Chappell and Haarhoff [2] state that, unlike the ammonium salts, the sodium and potassium salts of phosphoric and acetic acid do not undergo net translocation through the cristae membrane. According to the chemiosmotic hypothesis [5,7,8], Na+ and K+

The Sodium‐Induced Efflux of Calcium from Heart Mitochondria

“…The entry of Na' in exchange for H+ was first reported by Mitchell and Moyle [10,11] for liver mitochondria and attributed to the existence of a Na+-H+ antiporter. A similar exchange seems to exist in heart mitochondria.…”

Mitochondria metabolite transport

“…From these specific systems, the unspecific permeability of the inner membrane, which is similar to those of other "tight" biological membranes, such as erythrocytes, must be differentiated. The inner membrane is permeable to water, monovalent acids such as pyruvate, hydroxybutyrate, acetoacetate, acetate, fatty acid, and to some polarizable anions such as azide [171][172][173][174][175][176][177][178][179][180][181] Permeation of these substances has been followed by swelling methods or by their effects on the intramitochondrial components. A number of results indicate that most of the monovalent acids or anions may permeate in the undissociated form [S, 191. Although the undissociated fraction for the monovalent acids at pH 7 is in the order of 10s2 to 10s3, it is still much lower for the dicarboxylic acids (1 OS5 to 10-7) [ …”

Calcium transport in mitochondria

“…Mitchell and Moyle. [ 10] have established that chloride crosses the mitochondrial membrane slowly by electrogenic uniport and that thiocyanate does so rapidly. Acetate crosses the membrane either as acetic acid or on an acetate/hydroxide anti-porter, the net effect being the same in either case, i.e.…”