The effects of hypoxia on active ionic transport processes in the gill epithelium of hyperregulating crab, Carcinus maneas.

Effects of hypoxia on the osmorespiratory functions of the posterior gills of the shore crab Carcinus maenas acclimated to 12ppt seawater (DSW) were studied. Short-circuit current (Isc) across the hemilamella (one epithelium layer supported by cuticle) was substantially reduced under exposure to 1.6, 2.0, or 2.5mg O2/L hypoxic saline (both sides of epithelium) and fully recovered after reoxygenation. Isc was reduced equally in the epithelium exposed to 1.6mg O2/L on both sides and when the apical side was oxygenated and the basolateral side solely exposed to hypoxia. Under 1.6mg O2/L, at the level of maximum inhibition of Isc, conductance was decreased from 40.0mScm-2 to 34.7mScm-2 and fully recovered after reoxygenation. Isc inhibition under hypoxia and reduced 86Rb+ (K+) fluxes across apically located K+ channels were caused preferentially by reversible inhibition of basolaterally located and ouabain sensitive Na+,K+-ATPase mediated electrogenic transport. Reversible inhibition of Isc is discussed as decline in active transport energy supply down regulating metabolic processes and saving energy during oxygen deprivation. In response to a 4day exposure of Carcinus to 2.0mg O2/L, hemolymph Na+ and Cl- concentration decreased, i.e. hyperosmoregulation was weakened. Variations of the oxygen concentration level and exposure time to hypoxia lead to an increase of the surface of mitochondria per epithelium area and might in part compensate for the decrease in oxygen availability under hypoxic conditions.