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

POSADA, VELIA; BEAUGÉ, LUIS; BERBERÍAN, GRACIELA

ANNALS OF THE NEW YORK ACADEMY OF SCIENCES.

Año: 2007 vol. 1099 p. 171 - 174

0077-8923

Na+ gradient-dependent Ca2+- uptake, Ca2+ev -stimulated Ca2+- release and PtdIns-4,5-P2 binding to NCX1 as a function of [Ca2+]ev (extra-vesicular) were measured in inside-out sarcolemmal vesicles at different pHev´s. 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+- uptake examined as function of [Na+]ev indicate that this effects are related to H+ + Na+ synergic inhibition. Ca2+ev-stimulated Ca2+efflux indicate that the Ca2+ regulatory site is involved. Therefore, to display maximal affinity to Ca2+i, hight pHi and PtdIns -4,5-P2 binding to NCX1 are simultaneously need. In addition, H+ may influence the distribution, or the exposure, of Ptd Ins-4,5-P2 molecules in the vicinity of the exchanger since net synthesis of PtdIns -4,5-P2 was not influenced by pH.