Abstract
SUMMARYWe studied the transepithelial potential difference (TEPD) and 22Na flux across isolated perfused gills (anterior pair 5 and posterior pairs 6–8) of the crab Chasmagnathus granulatus acclimated to either hypo- or hyper-osmotic conditions.The gills of crabs acclimated to low salinity, perfused and bathed with 10 ‰ saline solutions, produced the following TEPDs (hemolymph side with respect to bath side): 0.4±0.7, –10.2±1.6, –10.8±1.3 and –6.7±1.3 mV for gills 5, 6, 7 and 8, respectively. Gills 6, 7 and 8 did not differ significantly. Reducing the saline concentration of bath and perfusate from 30 ‰ to 20 ‰ or 10 ‰ increased significantly the TEPDs of these gills. TEPDs of gill 6 (representative of posterior gills) were reduced by 69±5 % and 60±5 % after perfusion with ouabain or BaCl2 (5 mmol l–1 each), respectively. The same gill showed a net ouabain-sensitive Na+ influx of 1150±290 μequiv g–1 h–1.Gill 6 of crabs acclimated to high salinity produced TEPDs of –1.5±0.1 and –1.3±0.09 mV after perfusion with 30 ‰ or 40 ‰ salines, respectively. Perfusion with ouabain or BaCl2 reduced TEPDs by 76±7 % and 86±4 %, respectively. A net ouabain-sensitive Na+ efflux of 2282±337 μequiv g–1 h–1 was recorded in gill 6 perfused with 38 ‰ saline.
Highlights
Semiterrestrial estuarine crabs are adapted to a wide range of conditions
A net ouabain-sensitive Na+ efflux of 2282±337 μequiv g–1 h–1 was recorded in gill 6 perfused with 38 ‰ saline
Posterior gills of crabs acclimated to low salinity, perfused and bathed with identical salines, showed hemolymph-side negative transepithelial potential difference (TEPD), which increased significantly in absolute value as the concentration of saline solutions decreased; no significant TEPD was recorded in gill 5 (Fig. 1)
Summary
Semiterrestrial estuarine crabs are adapted to a wide range of conditions. Water salinity varies from full-strength seawater to almost freshwater in a geographical and tidal basis. Aerial ventilation may cause evaporative concentration of water retained within the branchial chambers, leading to hyper-saline exposure of the gills and the gill chamber epithelium (Schmitt and Santos, 1993). Terrestrial and semiterrestrial crabs of marine or estuarine origin possess hyper- and hypo-regulation capacities, showing little variation in their internal osmotic and ionic concentrations within a wide range of salinity (Gross, 1964; Mantel and Farmer, 1983; Schubart and Diesel, 1998, 1999). While anterior gills are lined with thin epithelium and have a mainly respiratory function, the posterior ones play a key role in compensatory active uptake of ions (Siebers et al, 1982; Gilles and Péqueux, 1986; Towle and Kays, 1986; Compère et al, 1989). There is much evidence from electrophysiological and ion flux studies on the ion-uptake capacity of posterior gills of different crab species (Gilles and Péqueux, 1981, 1985; Péqueux et al, 1988; Siebers et al, 1985; Lucu and Siebers, 1986; Burnett and Towle, 1990) (for a review, see Péqueux, 1995)
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