Neural Modulation Of Salt Secretion In Teleost Opercular Epithelium By α2-Adrenergic Receptors And Inositol 1,4,5-Trisphosphate

Opercular epithelia from seawater-adapted killifish (Fundulus heteroclitus) were dissected with the nerve intact, mounted in Ussing-style membrane chambers and bathed in symmetrical saline solutions. Nerve stimulation rapidly inhibited transepithelial current (a measure of Cl− secretion rate) by 27.3±3.3 % (N=22), and the effect could be sustained for more than 10 min using intermittent pulse trains at 10 Hz. The effect was blocked in a dose-dependent manner by yohimbine, but not by propranolol, atropine or tubocurarine, indicating mediation by α2-adrenergic receptors. The effect was also present, but significantly diminished, in opercular membranes from animals that had been transferred to sea water for 48 h (18±8.6 % inhibition, N=14). The resting current and the effect were absent in membranes from freshwater-adapted animals. The addition of clonidine (1.0 μmol l−1 serosal side) started to inhibit Cl− current after 40–60 s; immediately before this, at 30 s, there was a significant rise (P