AVT and IT regulate chloride secretion in the operculum of killifish Fundulus heteroclitus

Abstract

The killifish Fundulus heteroclitus is a euryhaline teleost with an unmatched capacity of salinity adaptation. In seawater, chloride secretion is the branchial driving force for removal exceso NaCl from the plasma. Previous studies in this species have used the opercular epithelium as a proxy for gill. Here, we assessed the actions of the neuropeptides arginine vasotocin (AVT) and isotocin (IT) mediated by their specific receptors (AVTRs and ITR) on the regulation of absorption/secretion in the killifish operculum in Ussing chambers. The opercular bioelectrical response to AVT treatment showed a clear two-phase response in short circuit current variation (DIsc, mAmp/cm2), with a short-term (~3 min) increase of absorptive processes and a subsequent stimulation (>3 min) of chloride secretion. V1 or V2 receptor antagonists totally and selectively inhibited either the absorptive or the secretory effect of AVT in Isc. In contrast, IT treatment only elicited a response in the chloride secretion. Our results demonstrate a regulatory role for the neuropeptides AVT and IT in the regulation of chloride secretion at putative physiological circulatory levels in seawater-acclimated teleost fishes.