Minor Contribution Of Ncx To Na+-Ca2+ Exchange Activity In Brain Mitochondria

NCLX was identified as a mitochondrial Na+-Ca2+ exchanger. However, contribution of NCLX to overall mitochondrial Na+-Ca2+ exchange activity remains unclear, especially in brain mitochondria where plasma membrane Na+-Ca2+ exchanger NCX also exists. We studied the issue using isolated mouse brain mitochondria. The Na+- as well as Li+-dependent Ca2+ efflux from mitochondria was significantly inhibited by a NCLX blocker, but was insensitive to NCX blockers, suggesting that NCLX comprises a major part in forward mode of mitochondrial Na+-Ca2+ exchange activity. On the other hand, the Na+-dependent Ca2+ influx into mitochondria, the reverse mode, was insensitive to all the blockers tested, suggesting unidentified Ca2+ transport systems.