Compartmentalized nitric oxide (NO) and superoxide anion formation in hypoxic mussel gills: effects on the mitochondrial electron transport system

DORIS ABELE; PAULA MARIELA GONZÁLEZ; GEORGINA RIVERA-INGRAHAM; IARA ROCCHETTA

Congreso; PHYSIOMAR 17; 2017

Nitric oxide (NO) is a signalling molecule witha variety of cellular functions and a reactive nitrogen species. Itsphysiological role in marine invertebrates is poorly understood. We studied formationof NO (DAF-2T fluorescence) and superoxide anion (MitoSOX) with live imagingtechniques during hypoxic exposure of Mytilusedulis gill filaments. Thirty minutes of exposure caused a 1.8 (7 kPa PO2)and 3-fold (1 kPa PO2) increase of NO generation in the muscularcells surrounding the hemolymphatic vessels of the gill filaments. This causeddilatation of blood vessel diameter by 36% (7 kPa) and 45% (1 kPa), which facilitatesblood flow. Superoxide formation within the filament epithelial cells increased1.8 (7kPa) and 2.4-fold (1 kPa). Biochemical analysis of mitochondrial electrontransport complexes in hypoxia exposed gill tissue indicates decreased activityof complexes I and III in both hypoxic conditions; whereas complex IV(cytochrome-c oxidase) activity increased at 7 kPa and decreased at 1 kPa comparedto normoxic controls. This corresponds to the pattern of PO2-dependentgill respiration rates recorded in ex-vivoexperiments (Rivera-Ingraham et al., 2013). Severe hypoxia (1 kPa) appears tohave a stabilizing effect on NO concentration, since less oxygen is availablefor its oxidation to NO2/NO3. Hypoxia thus supports the NO dependent inhibitionof complex IV activity, a mechanism that could fine tune mitochondrialrespiration to the local oxygen availability in the tissue. Experiments inwhich we applied the chemical NO-donor SperminNONOate (concentrations rangingfrom 1 to 6 mM) under normoxic conditions corroborate the dilatational effectof NO on the blood vessel. Our study highlights a basal function of NO inimproving perfusion of hypoxic invertebrate tissues, a model for the well-knowntreatment of coronary ischaemia and ?chest pain? in human pathology since the19th century.