Regulation of Mitochondrial Nitric Oxide Synthase in Endotoxemia

LISDERO C; BOCZKOWSKI J; CARRERAS MC; PODEROSO JJ

San Francisco, EEUU

Congreso; First International Conference Biology, Chemistry ad Therapeutic Applications of Nitric Oxide; 2000

NO Society

Recently, two different groups reported the presence of NOS in rat liver mitochondria (mtNOS). This mtNOS exhibited epitope homology with iNOS, but its activity was Ca2+ dependent. Since mitochondria are particularly affected by iNOS-produced nitric oxide and derived peroxynitrite, the aim of the study was to analyze mtNOS expression in endotoxemia. For that purpose, expression and activity of mtNOS were measured 24 h after 2 mg/Kg i.p. inoculation of E.coli LPS. The results confirmed that mtNOS is constitutively expressed in rat liver and heart mitochondria. However, in liver,  it showed  a molecular weight of about 150 KDa and resulted clearly distinguished from 130 KDa classic iNOS  and was also recognized by anti eNOS antibodies . Moreover, mtNOS was present in homozygous iNOS knock-out mice. After LPS, mtNOS activity and expression were increased by two fold, compared with controls (40 ±3 vs. 20 ± 5 pmol [3H]-citrulline / min mg prot, respectively, p< 0.05). Classic iNOS was not detected in control mitochondria but, together with mtNOS, appeared in the organelles during endotoxemia. In this situation, mitochondrial oxygen uptake was clearly modulated by addition of L-arginine or L-NMMA. It is concluded that constitutive mtNOS, a variant possibly produced by alternative splicing of a NOS isoform other than iNOS, is under regulation by cytokines in endotoxemia