Ventilatory responses of the Atlantic blue crab, Callinectes sapidus, to hypoxia and hydrogen sulfide exposure

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Derex, Rebecca Lynn
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In coastal estuaries all over the world, hypoxic zones are increasing in number and severity with heavy implications on coastal management and ecosystem health. Crustaceans have evolved complex physiological responses to environmental hypoxia including the alteration of ventilatory patterns upon acute exposure to hypoxic conditions. An increasing body of evidence suggests that endogenously produced H2S mediates vertebrate O2 sensing, but the underlying molecular mechanism of environmental O2 sensing in invertebrates has yet to be described. This study compared the effects of environmental hypoxia (6.7 and 10 kPa Po2) and exogenous H2S concentrations (0, 1, 5, 10, 25, and 50 mM) on ventilation in the blue crab Callinectes sapidus. Additionally, inhibitors of H2S-producing enzymes cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) were administered prior to severe hypoxic exposure in an attempt to dampen the ventilatory response. We confirmed previous findings that hypoxia elicits increases in ventilatory activity and decreases ventilatory pausing behaviors, and these effects were mimicked by exposure to low doses of H2S. Higher doses of H2S elicited different ventilatory patterns that may indicate toxicity. CBS and CSE inhibitors altered ventilatory pause patterns under normoxic conditions, but did not effectively inhibit the ventilatory hypoxic response. The present study provides evidence that at low doses, H2S elicits similar ventilatory responses in blue crabs to those of hypoxic exposures; however, stronger evidence is required to definitively implicate H2S as a crustacean cellular oxygen sensor.
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