Atriopeptin II stimulates chloride secretion in the isolated operculum epithelium of Fundulus heteroclitus

Whole killifish efflux of 36Cl was increased more than 2x with the addition of 1.4 x 10-7 M atriopeptin (ANF) to the seawater bath. Atriopeptin II (10-7 M) added serosally to the isolated Fundulus heteroclitus opercular epithelium resulted in a consistent stimulation of the short-circuit current, from 129.5 +/- 12.3 to 153.5 +/- 13.4 μA/cm2. Tissue resistance was decreased 10% from 114.9 +/- 14.2 to 103.9 +/- 11.8 Omega x cm2 indicating a change in chloride conductance. The effect of ANF was maximal at 10-7M and mucosal addition of ANF was ineffective in stimulating the opercular current. The ANF current stimulation did not interfere with the isoproterenol (10-6 M) response but ANF did not stimulate the current if added after isoproterenol. Serosal addition of propranolol (10-5 M), sufficient to inhibit 10-6 M isoproterenol, had no effect on the ANF response. The serosal addition of 10-6 M tetrodotoxin or 10-4 M diltiazem did not inhibit the ANF response. The stimulatory effect observed by ANF did not involve the isoproterenol receptor or nerve activation; however, it was a distinct stimulatory response on the isolated opercular epithelium