An anion channel in guinea pig gallbladder epithelial cells is highly permeable to HCO(-)(3).
In guinea pig gallbladder epithelium, a secretion of fluid, secondary to an electrogenic secretion of Cl(-) and HCO(-)(3), is elicited in the presence of a high intracellular concentration of adenosine 3'-5'-cyclic monophosphate (cAMP). The aim of this study was to analyze the effects of secretagogues on the activity of anionic channels in isolated epithelial cells using the patch-clamp technique and measuring the electrical potential difference of the cellular membrane (pd(cm)). In cell-attached configuration, with the microelectrode filled with a solution of N-methylglucamine-Cl, or in inside-out configuration (symmetrical solution), it was possible to demonstrate the presence of an 18-pS Cl(-) channel with linear current/voltage (I/V) relationship and voltage independence; this channel is not activated by cAMP (cell-attached configuration). In inside-out configuration (symmetrical solution), another anionic channel with a conductance of 2.8 pS, voltage independence, and a linear I/V relationship was also identified. This channel was stimulated by cAMP (cell-attached configuration) and by PKA + ATP + cAMP (inside-out configuration). The channel was inhibited by NPPB (10(-5) M), but not by other anionic inhibitors. Measurements of the pd(cm) value suggested that in isolated cells, as in whole tissue, cAMP activates conductance for both Cl(-) and HCO(-)(3). The selectivity of the channel was gluconate < SO(2-)(4) < Cl(-) < Br(-) < I(-) < HCO(-)(3) < SCN(-) and the P(HCO(3))/P(Cl) was 2.6. Some features of the channel resemble those of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel and RT-PCR performed on mRNA from isolated epithelial cells detected the presence of a CFTR homologue mRNA. The results obtained indicate that this channel is responsible for the HCO(-)(3) conductance activated by cAMP.
Meyer
G
G
Dipartimento di Fisiologia e Biochimica Generali, Sezione di Fisiologia Generale, Università degli Studi di Milano, Via Celoria 26, Milan, I-20133, Italy. Giuliano.meyer@unimi.it
Garavaglia
M L
ML
Bazzini
C
C
Bottà
G
G
D000818:Animals; D000838:Anions; D001483:Base Sequence; D001639:Bicarbonates / Q000378:metabolism*; D002463:Cell Membrane Permeability; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism; D005704:Gallbladder / Q000378:metabolism*; D006168:Guinea Pigs; D015640:Ion Channel Gating; D007473:Ion Channels / Q000378:metabolism*; D017136:Ion Transport; D008564:Membrane Potentials; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques
D000838:Anions; D001639:Bicarbonates; D007473:Ion Channels; D019005:Cystic Fibrosis Transmembrane Conductance Regulator