Changes in the electrophysiological parameters of the posterior intestine of Anguilla anguilla (Pisces) induced by oxytocin, urotensin II and aldosterone

ABSTRACT

In view of the importance of the intestine in the osmoregulation of freshwater fishes, we determined the effects of oxytocin, urotensin II (UII), and aldosterone added to the serosal side of the isolated posterior intestine of the freshwater-adapted teleost Anguilla anguilla on electrophysiological parameters. Oxytocin decreased the short-ciruit current (SCC) and transepithelial potential difference (TPD) at a centrations of 1 and 10 mU/ml (to 50 per cent and 42 per cent of control values, respectively), but did not alter these parameters at a concentration of 0.1 mU/ml. UII reduced SCC and TPD at concentrations of 10 nM, 50nM and 100 nM (to 85 per cent of control values), but increased these parameters at the concentration of 500 nM (to 115 per cent of control values). Aldosterone did not alter SCC or TPD at the concentrations tested (10 nM and 100 nM). Oxytocin may open Na+ channels in the apical membrane, allowing the flow of Na+ to the serosa, reduced SCC and TPD. Should this hypothesis be correct, oxytocin would be important for freshwater adaptation, since it would increase absorption. The reduction of SCC and TPD in the posterior intestine A. anguilla induced by UII is evidence that this neurohormone is also important for freshwater adaptation in teleosts. Aldosterone did not show this effect probaly due to the lack of receptors in this organ.