Sensitivity of mitochondrial Mg++ flux to reagents which affect K+ flux.
Effects on Mg++ transport in rat liver mitochondria of three reagents earlier shown to affect mitochondrial K+ transport have been examined. The sulfhydryl reactive reagent phenylarsine oxide, which activates K+ flux into respiring mitochondria, also stimulates Mg++ influx. The K+ analog Ba++, when taken up into the mitochondrial matrix, inhibits influx of both K+ and Mg++. The effect on Mg++ influx is seen only if Mg++, which blocks Ba++ accumulation, is added after a preincubation with Ba++. Thus the inhibition of Mg++ influx appears to require interaction of Ba++ at the matrix side of the inner mitochondrial membrane. Added Ba++ also diminishes observed rates of Mg++ efflux but not K+ efflux. This difference may relate to a higher concentration of Ba++ remaining in the medium in the presence of Mg++ under the conditions of our experiments. Pretreatment of mitochondria with dicyclohexyl-carbodiimide (DCCD), under conditions which result in an increase in the apparent Km for K+ of the K+ influx mechanism, results in inhibition of Mg++ influx from media containing approximately 0.2 mM Mg++. The inhibitory effect of DCCD on Mg++ influx is not seen at higher external Mg++ (0.8 mM). This dependence on cation concentration is similar to the dependence on K+ concentration of the inhibitory effect of DCCD on K+ influx. Although mitochondrial Mg++ and K+ transport mechanisms exhibit similar reagent sensitivities, whether Mg++ and K+ share common transport catalysis remains to be established.
Diwan
J J
JJ
Biology Department, Rensselaer Polytechnic Institute, Troy, New York 12180-3590.
Haley
T
T
Moore
C
C
D000818:Animals; D001152:Arsenicals / Q000494:pharmacology; D001464:Barium / Q000378:metabolism; D001693:Biological Transport, Active / Q000187:drug effects; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism*; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D051381:Rats
D001152:Arsenicals; C029341:oxophenylarsine; D001464:Barium; D004024:Dicyclohexylcarbodiimide; D008274:Magnesium; D011188:Potassium