Low-conductance anion channel activated by cAMP in teleost Cl- -secreting cells

We studied characteristics and modulation of ion channels in primary cultures of opercular epithelium from the euryhaline marine killifish Fundulus heteroclitus. Primary cultures, 17-28 h old, retain mitochondria-rich Cl- cells identifiable by fluorescence microscopy. Cell-attached patches revealed frequent low-conductance 8.1 +/- 0.35 pS channels that usually became inactive on excision; high-conductance anion channels were not apparent. Ion substitution experiments demonstrated selectivity for Cl- over gluconate of 1:0.07. With addition of 1-isobutyl-3-methylxanthine (0.1 mM) and dibutyryladenosine 3',5'-cyclic monophosphate (1.0 mM) to the bath, incidence of the channel increased from 35.3 to 61.9% of total patches (n = 156 and 21, respectively), and incidence of patches with multiple copies of the channel increased markedly from 2.2 to 38.5%. Epithelial Cl- transport was inhibited by mucosally added diphenylamine-2-carboxylic acid (1.0 mM) but not by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (0.1-1.0 mM). The anion channel was absent from cultured killifish corneal epithelium, a tissue that lacks Cl- cells. We conclude that a low-conductance anion channel of Cl- cells, likely in the apical membrane, may account for adenosine 3',5'-cyclic monophosphate-activated Cl- secretion by marine fish.