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)
Kunzelmann
K
K
Physiologisches Institut, Albert-Ludwigs-Universität Freiburg, Germany.
Koslowsky
T
T
Hug
T
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Gruenert
D C
DC
Greger
R
R
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