Effects of CdCl2 on electrophysiological parameters in the intestine of the teleost fish, Anguilla anguilla

In the present study the action of cadmium, a well known environmental pollutant, on the salt absorptive function of the eel, Anguilla anguilla, intestine was evaluated by estimating the rate of net Cl- absorption expressed as short circuit current (I-sc, mu A cm(-2)). In tissues mounted on Ussing chamber, I-sc and transepithelial potential difference (V-t, mV) responded in a concentration dependent manner to the addition of CdCl2 to the serosal or mucosal V-t (90% inhibition) after 1 h of incubation was obtained at a concentration of 100 mu M from the serosal side and 5 mM from the mucosal one. To understand the nature of I-sc inhibition induced by cadmium, the response of electrical parameters to the heavy metal exposure was examined in tissues exposed to different substances known to block Cl- transport at different cellular levels. Hence, bumetanide, which is known to inhibit Cl- transport by blocking the luminal Na+-K+-2Cl(-) cotransporter and Cl--conductive channels at the basolateral membrane of the enterocyte, added to the mucosal (10 mu M) or the serosal solution (100 mu M), abolished the response of I-sc and V-t to CdCl2 treatment. Similar results were obtained when tissues were pre-treated with ouabain (serosal, 100 mu M) or when Na+ or Cl- were omitted from the bathing media. Furthermore, cadmium alters the permselectivity of the tight junctions since the magnitude of the diffusion potential evoked by an imposed serosa-mucosa NaCl gradient (2:1) was strongly reduced by addition of CdCl2 to either serosal or mucosal solution. Microelectrode experiments point to a relative impermeability of the luminal membrane to the heavy metal since the luminal membrane potential (V-m) remains unchanged during perfusion with CdCl2. The results suggest that cadmium acts on the transport process responsible for Cl--absorption in eel intestine. Therefore, one of the factors contributing to the toxic effect of cadmium on fish could be related to the ion-balance disturbances of body fluids subsequent to the altered osmoregulatory function of the intestine in marine teleosts. (C) 1998 Elsevier Science B.V. All rights reserved.