Regulation of phosphatydilinositol 4,5-biphosphate bound to the bovine cardiac Na+/Ca2+ exchanger

LUIS BEAUGÉ, CARLA ASTEGGIANO AND GRACIELA BERBERIÁN.

“Sodium-Calcium Exchange”.

Año: 2002; p. 418 - 420

Abstract: Western blot and cross immunoprecipitation analysis with specific antibodies demonstrate that in bovine heart sarcolemmal vesicles phosphati-dylinositol-4,5-biphosphate (Ptdlns-4,5-P2) binds strongly to the Na+/Ca2+ei-changer (NCX1). This binding is modulated by ATP, Ca2+, vanadate. exchanger inhibitory peptide (XIP), and PLC-Ptdlns specific in a way resembling the ATP regulation of the exchange fluxes. With 1 mM Ca2+, 3 mM Mg2 and 0.4 mM vanadate, 1 mM ATP increased about twofold the bound Ptdlns-4,5-P2, reaching a steady state in 3-5 s at 37°C. With 100 jlM Ca2+, ATP had no effect on the PtdIns-4,5-P2 bound to NCX1 or on the exchange fluxes. With-out vanadate the bound PtdIns-4,5-P2 was largely reduced; under this condition ATP failed to increase it and did not stimulate the exchanger. XIP inhibit the exchanger, more noticeable in the absence of ATP. With XIP, ATP does nol modify the levels of bound Ptdlns-4,S-P2; however there is a small but distinct ATP stimulation of the exchanger. Vesicles pretreated with Ptdlns-PLC, showed no de novo, |32PjATP-induced, production of PtdIns-4,5-P2, but some ATP-stimulated increase in the bound Ptdlns-4,5-P2 was detected; however, that increase did not exceed the levels found with vanadate and no ATP. These results indicate that in bovine heart sarcolemmal vesicles, ATP up-regulation of NCX1 is related to PtdIns-4,5-P2 bound to the exchanger, perhaps over t "threshold" or "unspecific" amount. In addition, vanadate could influence the amount of detected PtdIns-4,5-P2 either by inhibiting phosphoinositide-specific phosphatases and/or by inducing a redistribution of PtdIns-4,5-P2 molecule associated with the Na+/Ca2+ exchanger. Keywords: Na+/Ca2+ exchanger; bovine heart; phosphoinositides; metabolic regulation; ATP; XIP; vanadate