Phosphatidyl inositol-4,5-bisphosphate bound to bovine cardiac Na+/Ca2+ exchanger displays a MgATP regulation similar to that of the exchange fluxes.
This work shows the existence of a phosphatidylinositol 4,5-bisphosphate (PtdIns-4,5-P2) bound form of the cardiac sarcolemmal Na+/Ca2+ exchanger. That was demonstrated in Western blots and cross-immunoprecipitation by using specific antibodies against the NCX1 exchanger (NCX1) and against PtdIns-4,5-P2. In addition, PtdIns-4,5-P2 bound to the Na+/Ca2+ exchanger and the Na+/Ca2+ exchange fluxes displayed a similar MgATP regulation: (a) both increase by 100-130% when membrane vesicles are incubated (15-20 s at 37 degrees C) with 1 mM MgATP and 1 microM Ca2+ (b) in the presence of 100 microM Ca2+, MgATP fails to stimulate the exchange fluxes and does not modify the levels of PtdIns-4,5-P2 bound to the exchanger. In addition, in the absence of Ca2+, the net synthesis of total membrane PtdIns-4,5-P2 is greatly reduced compared with that in the presence of 1 microM Ca2+. Furthermore, in the absence of Ca2+ there is no effect of MgATP on the levels of PtdIns-4,5-P2 bound to the exchanger. These results indicate that, in bovine heart, MgATP-stimulation of Na+/Ca2+ exchange is associated with intracellular Ca2+-dependent levels of PtdIns-4,5-P2 bound to the exchanger molecule.
Asteggiano
C
C
Laboratorio de Biofísica, Instituto de Investigación Médica Mercedes y Martín Ferreyra (INIMEC-CONICET), Casilla de Correo 389, 5000 Córdoba, Argentina.
Berberián
G
G
Beaugé
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L
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D009206:Myocardium / Q000378:metabolism*; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D010743:Phospholipids / Q000302:isolation & purification; D012508:Sarcolemma / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism
D019269:Phosphatidylinositol 4,5-Diphosphate; D010743:Phospholipids; D019831:Sodium-Calcium Exchanger; C110374:sodium-calcium exchanger 1; D000255:Adenosine Triphosphate; D012964:Sodium; D002118:Calcium