Ionic Selectivity of NCKX2, NCKX3, and NCKX4 for Monovalent Cations at K~+-Binding Site

摘要

To determine the ionic selectivity of K~+-sites in three members of Na~+/Ca~(2+)+K~+ exchanger (NCKX) family: NCKX2, NCKX3 and NCKX4, we compared the amplitudes of reverse mode NCKX current (I_(nckx)) activated by K~+-substitutes (Rb~+, NH_4~+, Cs~+, or Li~+) relative to that by K~+ in an HEK293 cell overexpressing each of NCKX isoforms. In all three isoforms, monovalent cations activated I_(nckx) with similar order of potency: K~+ > Rb~+ > NH_4~+ > Cs~+ Li~+. However, the relative potency of Cs~+ and NH4~+ for activating NCKX2 was significantly higher than those for NCKX3 and NCKX4, indicating that the selectivity of NCKX2 for K~+ is weaker than the other two isoforms.