Molecular characterization, functional expression and tissue distribution of a second NCKX Na+/Ca2+ -K+ exchanger from Drosophila.

The Na+/Ca2+ -K+ exchanger (NCKX) utilizes the inward Na+ gradient and the outward K+ gradient to promote Ca2+ extrusion from cells. Here, we have characterized a second NCKX from Drosophila. Based on its chromosomal location (X chromosome) we have named it Ncxk-x. Three splice variants were isolated with three distinct N-terminal sequences. NCKX-X differs from NCKX proteins described so far in other species by lacking an N-terminal signal peptide. Heterologous expression of the respective cDNA's resulted in NCKX-X protein expression and K+ -dependent Na+/Ca2+ exchange activity for two of the three splice variants. Transcript localization of Nckx-x was investigated and compared with that previously described by us for Nckx30C.