J. Huschenbett et al., SENSITIVITY OF THE SYNAPTIC MEMBRANE NA+ CA2+ EXCHANGER AND THE EXPRESSED NCX1 ISOFORM TO REACTIVE OXYGEN SPECIES/, Biochimica et biophysica acta. Biomembranes, 1374(1-2), 1998, pp. 34-46
Two plasma membrane proteins, the Na+/Ca2+ exchanger (NCX) and the Ca2
+-ATPase, are major regulators of free intraneuronal Ca2+ levels as th
ey are responsible for extrusion of Ca2+ from the intracellular to the
extracellular medium. Because disruption of cellular Ca2+ regulation
plays a role in damage occurring under conditions of oxidative stress,
studies were conducted to assess the sensitivity of the NCX to reacti
ve oxygen species (ROS), Exchanger activity in brain synaptic plasma m
embranes and in transfected CHO-K1 cells was inhibited following brief
exposure to the peroxyl radical generating azo initiator 2,2'-azobis(
2-amidinopropane)dihydrochloride (AAPH) and to peroxynitrite. Incubati
on with hydrogen peroxide did not alter NCX activity, even at 800 mu M
concentration. In CHO-K1 cells transiently transfected with the NCX1
isoform of the exchanger, AAPH treatment decreased the maximal transpo
rt capacity (V-max), whereas the K-act remained unchanged. Peroxynitri
te led to an increase in K-act with no change in V-max. Loss of activi
ty following exposure to either AAPH or peroxynitrite was associated w
ith the formation of high molecular weight aggregates of NCX, and AAPP
H also caused fragmentation of the exchanger protein. These findings s
uggest that the NCX is sensitive to biologically relevant ROS and coul
d be involved in the loss of Ca2+ homeostasis observed under oxidative
stress. 0005-2736/98/$ - see front matter (C) 1998 Elsevier Science B
.V. All rights reserved.