INVESTIGADORES
MANGIALAVORI Irene Cecilia
congresos y reuniones científicas
Título:
The Membrane Calcium Pump regulations by the cytosqueleton
Autor/es:
LAURA VANAGAS; IRENE MANGIALAVORI; ARIEL CARIDE; JUAN PABLO ROSSI
Reunión:
Congreso; 6th International Conferences of Biological Physics. ICBP; 2007
Institución organizadora:
Sociedad de Biofísica Argentina
Resumen:
Plasma membrane calcium pump (PMCA) is an
integral membrane protein that actively transports Ca2+ towards the
extra cellular milieu. PMCA is activated by acidic phospholipids and regulated
by protein kinases, but the main regulatory mechanism is mediated by the
binding of calmodulin (CaM). We have previously shown that specific activity of
Ca2+-ATPase of erythrocyte membranes, measured at concentrations
below 50 mg/ml of protein
increases steeply up to 3-5 times when the membrane protein concentration
decreases from 40 mg/ml to 1 mg/ml. The activation by dilution was
also observed during ATP-dependent Ca2+ uptake measurements into
inside-out vesicles from Sf9 cells which over-express the enzyme, confirming
that it is a property of PMCA. Dilution of the protein did not modify the
activation by ATP, Ca2+ or Ca2+-calmodulin, and is
present in different PMCA isoforms; however it cannot be observed when using a
solubilized highly-purified micellar PMCA preparation, indicating that
interaction of PMCA with other proteins is needed for the dilution effect.
Furthermore, when using 1 mg/ml Cytochalasin D on erythrocyte membranes under
conditions that promote the polymerization of actin, the activation at low
concentration of protein does not take place. (Vanagas L. et al, BBActa 1768
(2007) 1641-1649). Results in this work show that when using Cytochalasin D on
erythrocyte membranes in a medium with a low ionic strenghth and devoid of Mg2+
and K+ salts, a condition that induces depolymerization of
actin, the dilution effect is further increased. On the other hand, when
measured Ca2+-ATPase activity of a purified PMCA preparation by
continuously monitoring the release of inorganic phosphate, the addition of
monomeric actin to the reaction medium activated the ATP hydrolysis by the
enzyme. As far as the reaction of actin polymerization proceeded, Ca2+-ATPase
activity progressively decreased. These results are consistent with the
hypothesis that monomeric actin would be responsible for the activation
observed at low concentrations of membranes proposing that in diluted
samples, actin exists in short filaments or as monomers and oligomeric actin
would act as an inhibitor.