Two functional isoforms of the rat brain Na+-Ca2+ exchanger were isolated from a λZAP hippocampus cDNA library. The open reading frame of clone RBE-1 codes for a protein 935 amino acids long, and that of clone RBE-2 codes for a protein 958 amino acids long. Expression in HeLa cells of Na+ gradient dependent Ca2+ transport activity was determined following transfeetion of the cells with either RBE-1 or RBE-2. Both clones expressed proteins that exchange Na+ with Ca2+ in an electrogenic manner and none of them exhibited a dependency of the antiport on K+, since they transported Ca2+ in an Na+ gradient dependent manner in external choline chloride as well.
