title: Differing roles of mitochondrial nitric oxide synthase in cardiomyocytes and urothelial cells.
abstract: The existence of mitochondrial nitric oxide (NO) synthase (mtNOS) has been controversial since it was first reported in 1995. We have addressed this issue by making direct microsensor measurements of NO production in the mitochondria isolated from mouse hearts. Mitochondrial NO production was stimulated by Ca2+ and inhibited by blocking electrogenic Ca2+ uptake or by using NOS antagonists. Cardiac mtNOS was identified as the neuronal isoform by the absence of NO production in the mitochondria of mice lacking the neuronal but not the endothelial or inducible isoforms. In cardiomyocytes from dystrophin-deficient (mdx) mice, elevated intracellular Ca2+, increased mitochondrial NO production, slower oxidative phosphorylation, and decreased ATP production were detected. Inhibition of mtNOS increased contractility in mdx but not in wild-type cardiomyocytes, indicating that mtNOS may protect the cells from overcontracting. mtNOS was also implicated in radiation-induced cell damage. In irradiated rat/mouse urinary bladders, we have evidence that mitochondrially produced NO damages the urothelial "umbrella" cells that line the bladder lumen. This damage disrupts the permeability barrier thereby creating the potential to develop radiation cystitis. RT-PCR and Southern blot analyses indicate that mtNOS is restricted to the umbrella cells, which scanning electron micrographs show are selectively damaged by radiation. Simultaneous microsensor measurements demonstrate that radiation increases NO and peroxynitrite (ONOO-) production in these cells, which can be prevented by transfection with manganese superoxide dismutase (MnSOD) or instillation of NOS antagonists during irradiation or irradiation of bladders devoid of mtNOS. These studies demonstrate that mtNOS is in the cardiomyocytes and urothelial cells, that it is derived from the neuronal isoform, and that it can be either protective or detrimental.
authors.affiliation: Renal Electrolyte Division, University of Pittsburgh School of Medicine, A1224 Scaife Hall, Pittsburgh, PA 15261, USA. ajk5@pitt.edu
authors.forename: Anthony
authors.initials: A
authors.lastname: Kanai
authors.forename: Michael
authors.initials: M
authors.lastname: Epperly
authors.forename: Linda
authors.initials: L
authors.lastname: Pearce
authors.forename: Lori
authors.initials: L
authors.lastname: Birder
authors.forename: Mark
authors.initials: M
authors.lastname: Zeidel
authors.forename: Susan
authors.initials: S
authors.lastname: Meyers
authors.forename: Joel
authors.initials: J
authors.lastname: Greenberger
authors.forename: William
authors.initials: W
authors.lastname: de Groat
authors.forename: Gerard
authors.initials: G
authors.lastname: Apodaca
authors.forename: James
authors.initials: J
authors.lastname: Peterson
mesh_terms: D000818:Animals; D019610:Cytoprotection; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D008928:Mitochondria / Q000201:enzymology*; D032383:Myocytes, Cardiac / Q000201:enzymology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D011832:Radiation Injuries / Q000517:prevention & control; D013482:Superoxide Dismutase / Q000494:pharmacology; D001743:Urinary Bladder / Q000166:cytology / Q000201:enzymology; D019459:Urothelium / Q000166:cytology / Q000201:enzymology* / Q000528:radiation effects; D019323:omega-N-Methylarginine / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D019323:omega-N-Methylarginine; D019001:Nitric Oxide Synthase; D013482:Superoxide Dismutase