Characteristics and actions of NAD(P)H oxidase on the sarcoplasmic reticulum of coronary artery smooth muscle

Abstract

It has been reported that nonmitochondrial NAD(P)H oxidases make an important contribution to intracellular O₂⁻· in vascular tissues and, thereby, the regulation of vascular function. Topological analyses have suggested that a well-known membrane-associated NAD(P)H oxidase may not release O₂⁻· into the cytosol. It is imperative to clarify the source of intracellular O₂⁻· associated with this enzyme and its physiological significance in vascular cells. The present study hypothesized that an NAD(P)H oxidase on the sarcoplasmic reticulum (SR) in coronary artery smooth muscle (CASM) regulates SR ryanodine receptor (RyR) activity by producing O₂⁻· locally. Western blot analysis was used to detect NAD(P)H oxidase subunits in purified SR from CASM. Fluorescent spectrometric analysis demonstrated that incubation of SR with NADH time dependently produced O₂⁻·, which could be substantially blocked by the specific NAD(P)H oxidase inhibitors diphenylene iodonium and apocynin and by SOD or its mimetic tiron. This SR NAD(P)H oxidase activity was also confirmed by HPLC analysis of conversion of NADH to NAD⁺. In experiments of lipid bilayer channel reconstitution, addition of NADH to the cis solution significantly increased the activity of RyR/Ca²⁺release channels from these SR preparations from CASM, with a maximal increase in channel open probability from 0.0044 ± 0.0005 to 0.0213 ± 0.0018; this effect of NADH was markedly blocked in the presence of SOD or tiron or the NAD(P)H oxidase inhibitors diphenylene iodonium, N-vanillylnonanamide, and apocynin. These results suggest that a local NAD(P)H oxidase system on SR from CASM regulates RyR/Ca²⁺channel activity and Ca²⁺release from SR by producing O₂⁻·.