SULFIDE-STIMULATION OF OXYGEN-CONSUMPTION RATE AND CYTOCHROME REDUCTION IN GILLS OF THE ESTUARINE MUSSEL GEUKENSIA-DEMISSA

Organisms, such as the mussel Geukensia demissa, that inhabit high-sul fide sediments have mechanisms that impede sulfide poisoning of aerobi c respiration, Oxygen consumption rates (nO(2)) of excised ciliated gi lls from freshly collected G. demissa were stimulated 3-fold at sulfid e concentrations between 200 and 500 mu M and remained stimulated at 1 000 mu M. Maintenance of mussels in sulfide-free conditions resulted i n less stimulation of gill nO(2) at <500 mu M sulfide and inhibition b etween 500 and 1000 mu M sulfide, Gills of Mytilus galloprovincialis f rom a sulfide-free environment were inhibited by greater than or equal to 200 mu M sulfide, These results indicate that sulfide stimulation of nO(2) may be correlated to environmental exposure to sulfide. Serot onin, a neurohormonal stimulant of ciliary beating, further increased sulfide-stimulated nO(2), possibly in support of energy demand, Sulfid e-stimulated nO(2) was negligible in boiled gills and was 61% inhibite d by cyanide, implicating the participation of mitochondrial electron flux. Mitochondrial cytochromes c and oxidase oxidation/reduction stat e changed little at <500 mu M sulfide, but reduction occurred at 500-2 000 mu M sulfide, suggesting that although cytochrome oxidation/reduct ion state may be regulated in the face of increased electron flux, reg ulation may fail at inhibitory sulfide levels, Sulfide-stimulated nO(2 ) may represent a detoxification mechanism in G. demissa.