LOW-CONDUCTANCE ANION CHANNEL ACTIVATED BY CAMP IN TELEOST CL--SECRETING CELLS

We studied characteristics and modulation of ion channels in primary c ultures of opercular epithelium from the euryhaline marine killifish F undulus heteroclitus. Primary cultures, 17-28 h old, retain mitochondr ia-rich Cl- cells identifiable by fluorescence microscopy. Cell-attach ed patches revealed frequent low-conductance 8.1 +/- 0.35 pS channels that usually became inactive on excision; high-conductance anion chann els were not apparent. Ion substitution experiments demonstrated selec tivity for Cl- over gluconate of 1:0.07. With addition of 1-isobutyl-3 -methylxanthine (0.1 mM) and dibutyryladenosine 3',5'-cyclic monophosp hate (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 incide nce 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'-diisot hiocyanostilbene-2,2'-disulfonic acid (0.1-1.0 mM). The anion channel was absent from cultured killifish corneal epithelium, a tissue that l acks 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.