In bovine heart Na+/Ca2+ exchanger maximal Ca2+i affinity requires simultaneously high pHi and PtdIns-4,5-P2 binding to the carrier.
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.
Posada
Velia
V
Laboratorio de Biofísica, Instituto de Investigación Médica Mercedes y Martín Ferreyra (INIMEC-CONICET), Casilla de Correo 389, 5000 Córdoba, Argentina.
Beaugé
Luis
L
Berberián
Graciela
G
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D009206:Myocardium / Q000378:metabolism*; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D011485:Protein Binding; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*
D019269:Phosphatidylinositol 4,5-Diphosphate; D019831:Sodium-Calcium Exchanger; D002118:Calcium