CA2-TYPE AND MUTANT NA+-CA2+ EXCHANGERS( REGULATION OF CARDIAC WILD)

Cytoplasmic Ca2+ regulation of the cardiac Na+-Ca2+ exchanger was stud ied in the wild-type and in mutant exchangers at two highly acidic reg ions within the cytoplasmic loop. The exchanger was expressed in Xenop us occytes and inside-out membrane patches were made using the giant p atch method (pipette diameter 25-35 mu m). In the wild-type and all mu tants studied, cytoplasmic Ca2+ augmented the outward exchange current . Mutation of three consecutive aspartic acids (amino acids 446-448 an d 498-500) and a deletion of amino acids 450-456 decreased the affinit y of regulatory Ca2+. Current decay upon removing cytoplasmic 1 mu M C a2+ was faster in these mutants than the wild-type. These findings ind icate that the region is responsible for Ca2+ regulation.