Cyclic AMP stimulation of Cl super(-) secretion by the opercular epithelium: The apical membrane chloride conductance

Chloride secretion (Isc) by the opercular epithelium of the teleost, Fundulus heteroclitus , is stimulated by elevations in intracellular cyclic AMP (cAMP) elicited by beta -adrenergic agonists, such as isoproterenol, and is accompanied by a small but significant increase in the transepithelial conductance (Gt). In the present studies, the effects of Cu super(2+) on cAMP-elevated and cAMP-depleted epithelia were observed to define the actions of cAMP in this stimulatory process. Simultaneous super(22)Na and super(36)Cl unidirectional flux determinations indicated that the only effects of both isoproterenol and Cu super(2+) were on the active Cl-secretory flux. The results indicate that cAMP stimulation of Cl super(-) secretion involves only the active transcellular Cl super(-) pathway and is accomplished in part by an increase in a Cl super(-)-dependent, mucosal Cu super(2+)-inhibitable increase in the Gt, which is most likely localized to the apical membrane of the chloride cell.