A COMPARATIVE STUDY OF ROLE OF MITOCHONDRIA AND SARCOPLASMIC RETICULUM IN UPTAKE AND RELEASE OF CA++ BY RAT DIAPHRAGM

The respective importance of mitochondria and of sarcoplasmic reticulum in the uptake and maintenance of Ca++ by the isolated rat diaphragm has been compared. Diaphragms were incubated at 30° in conditions optimal for Ca++ uptake either by isolated mitochondria or by sarcoplasmic reticulum: more Ca++ was taken up from the “mitochondrial” medium. For maximal uptake, Pi and Mg++ were necessary; substitution of NaCl and KC1 with sucrose had no effect on the uptake. The uptake was markedly inhibited by uncouplers of oxidative phosphorylation, by respiratory inhibitors, and by lowering the temperature of the incubation medium to 0°; it was not affected by oligomycin, aurovertin, DCCD, nor by inhibitors of Ca++ transport in the isolated sarcoplasmic reticulum (ergotamine, ergobasinine, caffeine). The lack of effect of caffeine was not due to lack of penetration into the muscle. Permeability barriers for ergotamine and ergobasinine could not be excluded. The maintenance of Ca++ by the diaphragm was optimal in a medium contaming Pi and Mg++. Uncoupling agents and respiratory inhibitors accelerated the rate and extent of release of Ca++ by the diaphragm. Lowering the temperature of the incubation medium to 0°, or addition of oligomycin, aurovertin, DCCD, had no effect on the release. The release of Ca++ was also unaffected by ergotamine, ergobasinine, caffeine. The results suggest a role for mitochondria in the uptake and maintenance of Ca++ by the isolated diaphragm. Copyright © 1969 Wiley‐Liss, Inc.