In dialyzed squid axons oxidative stress inhibits the Na⁺/Ca²⁺ exchanger by impairing the Ca_i²⁺-regulatory site

Abstract

The Na+/Ca2+ exchanger, a major mechanism by which cells extrude calcium, is involved in several physiological and physiopathological interactions. In this work we have used the dialyzed squid giant axon to study the effects of two oxidants, SIN-1-buffered peroxynitrite and hydrogen peroxide (H2O2), on the Na+/Ca2+ exchanger in the absence and presence of MgATP upregulation. The results show that oxidative stress induced by peroxynitrite and hydrogen peroxide inhibits the Na+/Ca2+ exchanger by impairing the intracellular Ca2+ (Cai2+)-regulatory sites, leaving unharmed the intracellular Na+− and Ca2+−transporting sites. This effect is efficiently counteracted by the presence of MgATP and by intracellular alkalinization, conditions that also protect Hi+ and (Hi+ + Nai+) inhibition of Cai2+-regulatory sites. In addition, 1 mM intracellular EGTA reduces oxidant inhibition. However, once the effects of oxidants are installed they cannot be reversed by either MgATP or EGTA. These results have significant implications regarding the role of the Na+/Ca2+ exchanger in response to pathological conditions leading to tissue ischemia-reperfusion and anoxia/reoxygenation; they concur with a marked reduction in ATP concentration, an increase in oxidant production, and a rise in intracellular Ca2+ concentration that seems to be the main factor responsible for cell damage.

Role of Na+/Ca2+ Exchanger (NCX) in Modulating Postovulatory Aging of Mouse and Rat Oocytes

“…Many studies reveal that ROS inactivates NCX, leading to a rise in cytoplasmic Ca 2+ and subsequent cell dysfunction [57]. For instance, in dialyzed squid axons, oxidative stress inhibits NCX by impairing the intracellular Ca 2+ -regulatory site [58]. In cardiac myocytes exposed to ischemia/reperfusion, which produces a burst of oxygen radicals, the NCX can operate in the reverse mode causing Ca 2+ influx into the cytoplasm [59].…”

The Na+/Ca2+ exchanger in cardiac ischemia/reperfusion injury

“…ROS also gives rise to myocardial dysfunction in IR and are reported to alter NCX1 activity. DiPolo et al [35] have already demonstrated that oxidative stress inhibits the NCX by impairing the Cai 2+ -regulatory site in dialyzed squid axons. Soliman et al [36] used the patch-clamp technique to study the effects of the ROS, H 2 O 2 , on recombinant NCX1 splice variants.…”