Differential effects of superoxide and hydrogen peroxide on myogenic signaling, membrane potential, and contractions of mouse renal afferent arterioles

Myogenic contraction is the principal component of renal autoregulation that protects the kidney from hypertensive barotrauma. Contractions are initiated by a rise in perfusion pressure that signals a reduction in membrane potential (E-m) of vascular smooth muscle cells to activate voltage-operated Ca2+ channels. Since ROS have variable effects on myogenic tone, we investigated the hypothesis that superoxide (O-2(center dot-)) and H2O2 differentially impact myogenic contractions. The myogenic contractions of mouse isolated and perfused single afferent arterioles were assessed from changes in luminal diameter with increasing perfusion pressure (40-80 mmHg). O-2(center dot-), H2O2, and E-m were assessed by fluorescence microscopy during incubation with paraquat to increase O-2(center dot-) or with H2O2. Paraquat enhanced O-2(center dot-) generation and myogenic contractions (-42 +/- 4% vs. -19 +/- 4%, P < 0.005) that were blocked by SOD but not by catalase and signaled via PKC. In contrast, H2O2 inhibited the effects of paraquat and reduced myogenic contractions (-10 +/- 1% vs. -19 +/- 2%, P < 0.005) and signaled via PKG. O-2(center dot-) activated Ca2+-activated Cl- channels that reduced E-m, whereas H2O2 activated Ca2+-activated and voltage-gated K+ channels that increased E-m. Blockade of voltage-operated Ca2+ channels prevented the enhanced myogenic contractions with paraquat without preventing the reduction in E-m. Myogenic contractions were independent of the endothelium and largely independent of nitric oxide. We conclude that O-2(center dot-) and H2O2 activate different signaling pathways in vascular smooth muscle cells linked to discreet membrane channels with opposite effects on E-m and voltage-operated Ca2+ channels and therefore have opposite effects on myogenic contractions.