Plasma membrane calcium pump activity is affected by the membrane protein concentration. Evidence for the involvement of the actin cytoskeleton¨

VANAGAS, L.; ROSSI, R.C.; CARIDE, AJ; FILOTEO, A; STREHLER, E; ROSSI, J.P.F.C.

BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES

Elsevier

Año: 2007 vol. 1768 p. 1641 - 1649

0005-2736

Plasma membrane calcium pump activity is affected by the membrane protein concentration: Evidence for the involvement of the actin cytoskeleton. Vanagas L, Rossi RC, Caride AJ, Filoteo AG, Strehler EE, Rossi JP. IQUIFIB, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956 (1113) Buenos Aires, Argentina. Plasma membrane calcium pumps (PMCAs) are integral membrane proteins that actively expel Ca(2+) from the cell. Specific Ca(2+)-ATPase activity of erythrocyte membranes increased steeply up to 1.5-5 times when the membrane protein concentration decreased from 50 mug/ml to 1 mug/ml. The activation by dilution was also observed for ATP-dependent Ca(2+) uptake into vesicles from Sf9 cells over-expressing the PMCA 4b isoform, confirming that it is a property of the PMCA. Dilution of the protein did not modify the activation by ATP, Ca(2+) or Ca(2+)-calmodulin. Treatment with non-ionic detergents did not abolish the dilution effect, suggesting that it was not due to resealing of the membrane vesicles. Pre-incubation of erythrocyte membranes with Cytochalasin D under conditions that promote actin polymerization abolished the dilution effect. Highly-purified, micellar PMCA showed no dilution effect and was not affected by Cytochalasin D. Taken together, these results suggest that the concentration-dependent behavior of the PMCA activity was due to interactions with cytoskeletal proteins. The dilution effect was also observed with different PMCA isoforms, indicating that this is a general phenomenon for all PMCAs.