Effects of peroxide and superoxide on coronary artery: ANG II response and sarcoplasmic reticulum Ca2+ pump

The sarcoplasmic reticulum (SR) Ca2+ pump in membranes isolated from arterial smooth muscle is damaged by reactive oxygen species (ROS). Because angiotensin II (ANG II) contracts arterial smooth muscle by mobilizing intracellular Ca2+ concentrations ([Ca2+])i, we determined the effects of ROS pretreatment on ANG II-induced contractions in coronary artery rings and [Ca2+]i transients in smooth muscle cells (SMC) cultured from them. This experimental design eliminates direct ROS interference in assay solutions, thus monitoring only the tissue damage. Pretreating the arteries with peroxide inhibited the ANG II contractions with the concentration for half-maximal activation (K0.5) = 74 +/- 5 microM. Peroxide (250 microM) inhibited the contractions to ANG II and cyclopiazonic acid (CPA, SR Ca(2+)-pump inhibitor) by 78.3 +/- 5.1 and 67.4 +/- 6.3%, respectively, but did not significantly affect the contractions by 60 mM KCl. Pretreating SMC with peroxide inhibited the ANG II-induced increase in [Ca2+]i with K0.5 = 24 +/- 3 microM for peroxide. Peroxide (100 microM) inhibited the increase in [Ca2+]i in response to ANG II and CPA by 78.9 +/- 5.1 and 38.3 +/- 4.9%, respectively. The SR Ca(2+)-pump activity was also measured as the Ca(2+)-dependent formation of 115-kDa acylphosphate. Pretreating SMC with 100 microM peroxide inhibited the acylphosphate levels by 36.3 +/- 3.2%. Peroxide (100 microM) pretreatment of SMC did not significantly affect their ANG II binding.(ABSTRACT TRUNCATED AT 250 WORDS)