AVT and IT regulate ion transport across the opercular epithelium of killifish (Fundulus heteroclitus) and gilthead sea bream (Sparus aurata)

The regulatory role of arginine vasotocin (AVT) and isotocin (IT) in Cl- secretion was investigated with the short circuit current (Isc) technique in opercular epithelia of killifish (Fundulus heteroclitus) and gilthead sea bream (Sparus aurata). Sea bream operculum showed similar to 4-fold lower number of Na/K-ATPase immunoreactive cells and similar to 12-fold lower secretory current than the killifish. In sea bream opercular membranes, the basolateral addition of AVT (10(-6) M) significantly stimulated Cl- secretion, while IT (10(-6) M) was without effect. In killifish, IT produced an immediate dose-dependent stimulation of Cl- secretion with significant effect at doses >= 10(-7) M and stimulation maxima (Delta Isc similar to 25 mu A.cm(-2)) at 10(-6) M. The basolateral addition of bumetanide (200 mu M) abolished >75% of the effect of IT on Cl- secretion. In turn, AVT had a dual effect on killifish opercular Isc: an immediate response (similar to 3 min) with Isc reduction in an inverted bell-shaped dose-response manner with higher current decrease (-22 mu A.cm(-2)) at 10(-8) M AVT, and a sustained dose-dependent stimulation of Cl- secretion (stable up to 1 h), with a threshold significant effect at 10(-8) M and maximal stimulation (similar to 20 mu A.cm(-2)) at 10(-6) M. Both effects of AVT appear receptor type specific. The VI-receptor antagonist SR 49059 abolished Isc reduction in response to AVT, while the specific V2-receptor antagonist (Tolvaptan, 1 mu M) abolished the stimulatory action of AVT on Cl- secretion. According to these results, we propose a modulatory role for AVT and IT in Cl- (NaCl) secretion across the opercular epithelium of marine teleost. (C) 2014 Elsevier Inc All rights reserved.