The Biological Bulletin, Vol 191, Issue 3 421-430, Copyright © 1996 by Marine Biological Laboratory

PHYSIOLOGY

Sulfide-Stimulation of Oxygen Consumption Rate and Cytochrome Reduction in Gills of the Estuarine Mussel Geukensia demissa

R. W. Lee, D. W. Kraus and J. E. Doeller
Department of Biology, University of Alabama at Birmingham, 1300 University Boulevard, Birmingham, Alabama 35294-1170

Organisms, such as the mussel Geukensia demissa, that inhabit high-sulfide sediments have mechanisms that impede sulfide poisoning of aerobic respiration. Oxygen consumption rates (nO2) of excised ciliated gills from freshly collected G. demissa were stimulated 3-fold at sulfide concentrations between 200 and 500 {mu}M and remained stimulated at 1000 {mu}M. Maintenance of mussels in sulfide-free conditions resulted in less stimulation of gill nO2 at <500 {mu}M sulfide and inhibition between 500 and 1000 {mu}M sulfide. Gills of Mytilus galloprovincialis from a sulfide-free environment were inhibited by {ge}200 {mu}M sulfide. These results indicate that sulfide stimulation of nO2 may be correlated to environmental exposure to sulfide. Serotonin, a neurohormonal stimulant of ciliary beating, further increased sulfide-stimulated nO2, possibly in support of energy demand. Sulfide-stimulated nO2 was negligible in boiled gills and was 61% inhibited by cyanide, implicating the participation of mitochondrial electron flux. Mitochondrial cytochromes c and oxidase oxidation/ reduction state changed little at <500 {mu}M sulfide, but reduction occurred at 500-2000 {mu}M sulfide, suggesting that although cytochrome oxidation/reduction state may be regulated in the face of increased electron flux, regulation may fail at inhibitory sulfide levels. Sulfide-stimulated nO2 may represent a detoxification mechanism in G. demissa.

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