cAMP-dependent activation of ion conductances in bronchial epithelial cells.
The cAMP-dependent activation of Cl- channels was studied in a bronchial epithelial cell line (16HBE14o-) in fast and slow whole-cell, and cell-attached patch-clamp experiments. The cells are known to express high levels of cystic fibrosis transmembrane conductance regulator mRNA and protein. Isoproterenol, forskolin and histamine (all 10 mumol/l) reversibly and significantly depolarized the membrane voltage (Vm) and increased the whole-cell Cl- conductance significantly by 34.0 +/- 0.9 (n = 3), 18.1 +/- 2.7 (n = 50), and 25 +/- 4.5 (n = 37) nS respectively. The effect of histamine was blocked by cimetidine (10 mumol, n = 5) but not by diphenhydramine (10 mumol/l, n = 4), which suggests binding of histamine to H2 receptors. The forskolin-induced current was not inhibited significantly by 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (0.5 mmol/l, n = 9) nor glibenclamide (10 mumol/l, n = 3) and had an anion-permeability sequence of Cl = Br- > I- (n = 9). In cell-attached recordings forskolin (10 mumol/l) increased the conductance of the patched membrane from 65.5 +/- 13.6 pS to 150.8 +/- 33.2 pS (n = 30). Although the conductance was increased significantly, clear ion channel events occurring in parallel with the current activation were not detected in the cell-attached membrane. In 4 out of 30 cell-attached recordings single-channel currents were observed. These channels, with a single-channel conductance of about 6 pS, were already active before forskolin was added. No effect of forskolin on the channel amplitude, open probability or kinetics of these channels was observed.(ABSTRACT TRUNCATED AT 250 WORDS)
Physiologisches Institut, Albert-Ludwigs-Universität Freiburg, Germany.
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K
Kunzelmann
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Koslowsky
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T
Hug
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Gruenert
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R
Greger
D001980:Bronchi / Q000166:cytology / Q000502:physiology*; D002712:Chlorides / Q000502:physiology*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D004553:Electric Conductivity; D004848:Epithelium / Q000502:physiology; D006632:Histamine / Q000494:pharmacology; D006801:Humans; D007477:Ions; D007545:Isoproterenol / Q000494:pharmacology
D002712:Chlorides; D007477:Ions; D005576:Colforsin; D006632:Histamine; D000242:Cyclic AMP; D007545:Isoproterenol