Trasepithelial potential differences in isolated perfused gills of the hyper-hyporegulating crab Chasmagnathus granulatus (Grapsidae)

LUQUET C. M.; POSTEL U.; URCOLA M.R.; SIEBERS D.

Liege

Congreso; 21st Congress European Society Comparative Physiology and Biochemistry; 2000

European Society Comparative Physiology and Biochemistry

The principal role played by tbe giils in hyperegulatory ion uptake has been established in several crab species. In contrast, the possible role of these organs in hyporegulatory ion excretion remains unclear. In the present study we measure transepithelial potential differences (TEPD) in gills isolated from crabs acclimated to low and high salinity as an attempt to understand the physiological processes involved in hyper and hyporegulation in Chasmagnathus granulatus.Gilis 5, 6, 7 and 8 extracted from crabs acclimated to either dilute (l2?) or concentrated (45?) seawater were perfused under symmetrical conditions. TEPDs were measured with Ag/AgCl electrodes and agar bridges.Gills from 12%o crabs were perfused with 30, 20 and 10? salines, and specific inhibitors of transport proteins. Results were tested by repeated measures Anova. Hemolymph negative TEPDs increasing significantly at lower concentrations were recorded only for gills 6-8. TEPD values and effects of both saline concentration and transport inhibitors were similar in the three gills. Internally applied ouabain and BaCl2 produced significant and reversible reduction of the TEPDs, while no effect was evident for external BaCl2 or CsCl.Gills from 45? crabs were perfused with 30 and 40? salines. Small (1 - 2 mV) but consistent, inside negative TEPDs were recorded for gills 6-8. In most cases TEPDs were lower at 40 than at 30?. KCN and ouabain tested at 40? blocked the TEPDs almost completely. In a posterior experiment the saline concentration was increased gradually (30-32-34-36-38- 40?). A slight ascendant tendency with increasing concentration was evident in these conditions.It could be concluded that the three most posterior gills of C. granulatus actively uptake ions from the bath. The Na+ K+ ATPase and a K+ channel, both located in the basolateral membrane are clearly implicated. Isolated gills showed to be able to respond to the ion transport needs. The results obtained with high salinity acclimated crabs suggest hyporegulatory functions of posterior gills. However, this topic needs further investigation. The small values of TEPD recorded at high saline concentrations are possibly related with low paracellular resistance as could be interpreted from electron microscopy studies that show reduced septate junctions at high salinity.