Abstract
Na+ i-dependent Ca2+ uptake, Na+-dependent Ca2+ release, and PtdIns-4,5-P2 binding to Na+/Ca2+ exchanger (NCX1) as a function of extravesicular (intracellular) [Ca2+] were measured. Alkalinization increases Ca2+ i affinity and PtdIns-4,5-P2 bound to NCX1; these effects are abolished by pretreatment 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. Extravesicular Na+-stimulated and Ca2+-dependent Ca2+ efflux indicate the Ca2+ regulatory site is involved. Therefore, to display maximal affinity to Ca2+ i, PtdIns-4,5-P2 binding and deprotonation of NCX1 are simultaneously need.
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