CALCIUM EFFLUX MECHANISM IN SPERM MITOCHONDRIA

This paper reports an investigation on calcium efflux mechanism in ram sperm mitochondria. Energized sperm mitochondria take up Ca2+ via the ruthenium-red sensitive uniporter, and possess a ruthenium-red insens itive efflux mechanism. Extramitochondrial Na+ did not affect the rate of Ca2+ efflux indicating that Na+/Ca2+ exchange mechanism is not inv olved. Depolarization of inner mitochondrial membrane induced by the u ncoupler carbonylcyanide-p-trifluoromethoxyphenyl hydrazone (FCCP) or by the organomercurial SH-reagent mersalyl, causes high stimulation in Ca2+ efflux. This stimulated Ca2+ efflux determined in the presence o f ruthenium-red and phosphate, is not inhibited by cyclosporin A (CSA) , indicating that mitochondrial permeability transition pore (MTP) is not involved in this Ca2+ efflux mechanism. The stimulated Ca2+ efflux is inhibited by ADP or atractyloside suggesting that the Ca2+ transpo rt mechanism might be intrinsic to the ADP/ATP carrier (AAC). Thus, th e data indicate that sperm mitochondria contain a Ca2+ efflux mechanis m operated via AAC and regulated by mitochondrial membrane potential a nd by ADP concentration.