Possible role of carbonic anhydrase, V-H(+)-ATPase, and Cl(-)/HCO3- exchanger in electrogenic ion transport across the gills of the euryhaline crab Chasmagnathus granulatus.

We studied the participation of carbonic anhydrase (CA), V-H(+)-ATPase, and Cl(-)/HCO3- exchanger in electrogenic ion absorption through the gills of Chasmagnathus granulatus. CA activity was measured in anterior gills and posterior gills after acclimation to 2 per thousand, 10 per thousand, 30 per thousand (about seawater), and 45 per thousand salinity. The highest CA specific activity was detected in the microsomal fraction in anterior gills, and in the cytosolic fraction, in posterior ones. Both fractions were strongly induced by decreasing salinity only in posterior gills. Perfusion of posterior gills from crabs acclimated to either 2 per thousand or 10 per thousand with acetazolamide inhibited CA activity almost completely. In posterior gills from crabs acclimated to 2 per thousand and perfused with 20 per thousand saline (iso-osmotic for these crabs), acetazolamide reduced transepithelial potential difference (V(te)) by 47%, further addition of ouabain enhanced the effect to 88%. Acetazolamide had no effect in the same gills perfused with 30 per thousand saline (iso-osmotic for seawater acclimated crabs). Bafilomycin A1 and SITS (inhibitors of V-H(+)-ATPase and Cl(-)/HCO3-) reduced V(te) by 15-16% in gills perfused with normal 20 per thousand saline, and by 77% and 45%, respectively when they were applied in Na-free 20 per thousand saline, suggesting the participation of those transporters and cytosolic CA in electrogenic ion absorption.

Transepithelial potential differences and Na(+) flux in isolated perfused gills of the crab Chasmagnathus granulatus (Grapsidae) acclimated to hyper- and hypo-salinity.

We studied the transepithelial potential difference (TEPD) and (22)Na 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 per thousand 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 per thousand to 20 per thousand or 10 per thousand 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 BaCl(2) (5 mmol l(-1) each), respectively. The same gill showed a net ouabain-sensitive Na(+) influx of 1150+/-290 microequiv 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 per thousand or 40 per thousand salines, respectively. Perfusion with ouabain or BaCl(2) reduced TEPDs by 76+/-7 % and 86+/-4 %, respectively. A net ouabain-sensitive Na(+) efflux of 2282+/-337 microequiv g(-1) h(-1) was recorded in gill 6 perfused with 38 per thousand saline.