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

GONZÁLEZ, P.M.,; RIVERA-INGRAHAM, G.A.; ROCCHETTA, I.; ABELE, D.

Cambridge

Conferencia; Physiomar 17, The physiology of aquatic ectotherms in a changing world; 2017

Nitric oxide (NO) is a signalling molecule with a variety of cellular functions and a reactive nitrogen species. Its physiological role in marine invertebrates is poorly understood. We studied formation of NO (DAF‐2T fluorescence) and superoxide anion (MitoSOX) with live imaging techniques during hypoxic exposure of Mytilus edulis 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 muscular cells surrounding the hemolymphatic vessels of the gill filaments. This caused dilatation of blood vessel diameter by 36% (7 kPa) and 45% (1kPa), which facilitates blood flow. Superoxide formation within the filament epithelial cells increased 1.8 (7kPa) and 2.4‐fold (1 kPa). Biochemical analysis of mitochondrial electron transport complexes in hypoxia exposed gill tissue indicates decreased activity of complexes I and III in both hypoxic conditions; whereas complex IV (cytochrome‐c oxidase) activity increased at 7 kPa and decreased at 1 kPa compared to normoxic controls. This corresponds to the pattern of PO2‐dependent gill respiration rates recorded in ex‐vivo experiments (Rivera‐Ingraham et al., 2013). Severe hypoxia (1 kPa) appears to have a stabilizing effect on NO concentration, since less oxygen is available for its oxidation to NO2/NO3. Hypoxia thus supports the NO dependent inhibition of complex IV activity, a mechanism that could fine tune mitochondrial respiration to the local oxygen availability in the tissue. Experiments in which we applied the chemical NO‐donor SperminNONOate (concentrations ranging from 1 to 6 mM) under normoxic conditions corroborate the dilatational effect of NO on the blood vessel. Our study highlights a basal function of NO in improving perfusion of hypoxic invertebrate tissues, a model for the well‐known treatment of coronary ischaemia and ?chest pain? in human pathology since the 19th century.