Superoxide release is involved in membrane potential changes in mouse peritoneal macrophages

The small G-protein Rac mediates depolarization-induced superoxide formation in human endothelial cells

Superoxide anions impair nitric oxide-mediated responses and are involved in the development of hypertensive vascular hypertrophy. The regulation of their production in the vascular system is, however, poorly understood. We investigated whether changes in membrane potential that occur in hypertensive vessels modulate endothelial superoxide production. In cultured human umbilical vein endothelial cells, changes in membrane potential were induced by high potassium buffer, the non-selective potassium channel blocker tetrabutylammonium chloride (1 mm), and the non-selective cation ionophore gramicidin (1 micrometer). Superoxide formation was significantly elevated to a similar degree by all three treatments (by approximately 60%, n = 23, p < 0.01), whereas hyperpolarization by the K(ATP) channel activator Hoe234 (1 micrometer) significantly decreased superoxide formation. Depolarization also induced an increased tyrosine phosphorylation of several not yet identified proteins (90-110 kDa) and resulted in a significant increase in membrane association of the small G-protein Rac. Accordingly, the Rac inhibitor Clostridium difficile toxin B blocked the effects of depolarization on superoxide formation. The tyrosine kinase inhibitor genistein (30 micrometer, n = 15) abolished depolarization-induced superoxide formation and also prevented depolarization-induced Rac translocation associated with it. It is concluded that depolarization is an important stimulus of endothelial superoxide production, which involves a tyrosine phosphorylation-dependent translocation of the small G-protein Rac.

Roles of reactive oxygen species: signaling and regulation of cellular functions

Reactive oxygen species (ROS) are the side products (H2O2, O2.-, and OH.) of general metabolism and are also produced specifically by the NADPH oxidase system in most cell types. Cells have a very efficient antioxidant defense to counteract the toxic effect of ROS. The physiological significance of ROS is that ROS at low concentrations are able to mediate cellular functions through the same steps of intracellular signaling, which are activated by natural stimuli. Moreover, a variety of natural stimuli act through the intracellular formation of ROS that change the intracellular redox state (oxidation-reduction). Thus, the redox state is a part of intracellular signaling. As such, ROS are now considered signal molecules at nontoxic concentrations. Progress has been achieved in studying the oxidative activation of gene transcription in animal cells and bacteria. Changes in the redox state of intracellular thiols are considered to be an important mechanism that regulates cell functions.