MAXIMAL Ca2+i AFFINITY OF BOVINE HEART Na+/Ca2+ EXCHANGER REQUIRES SIMULTANEOUSLY HIGH pHi AND PtdIns-4,5-P2 BINDING TO THE CARRIER

POSADA, VELIA; BEAUGÉ, LUIS; BERBERÍAN, GRACIELA

Bruselas - Belgica

Conferencia; Fifth International Conference:Sodium–Calcium Exchange and the Plasma Membrane Ca2+-ATPase in Cell Function; 2006

Na+ gradient-dependent Ca2+- uptake, Ca2+ev -stimulated Ca2+- release and PtdIns-4,5-P2 binding to NCX1 as a function of extra-vesicular (ev) [Ca2+] were measured in inside-out sarcolemmal vesicles. Alkalinization increases Ca2+i affinity and PtdIns-4,5-P2 bound to NCX1; these effects are abolished by pre-treatment with PtdIns-PLC and are insensitive to MgATP. Acidification reduces Ca2+i affinity. MgATP reverts it only partially despite the fact that the PtdIns-4,5-P2 bound to NCX1 reaches the same levels as at pH 7.8. Ca2+ev-stimulated Ca2+efflux indicate that the Ca2+ regulatory site is involved. Therefore, to display maximal affinity to Ca2+i, PtdIns -4,5-P2 binding and alkalinization are simultaneously need.