ISSN:
1432-2013
Keywords:
Bicarbonate permeability
;
Bicarbonate conductance
;
Cl− channels
;
HT29
;
T84
;
Respiratory cells
;
Bicarbonate channel
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract Bicarbonate permeability of epithelial chloride channels has been studied using the patch-clamp technique. The experiments were performed in excised insideout oriented membrane patches from three different cultured cell types: (a) HT29 colon carcinoma cell line, (b) T84 colon carcinoma cell line, and (c) respiratory epithelial cells (REC) in primary culture. In all three preparations we observed outwardly rectifying chloride channels with similar conductances with 145 mmol/l NaCl solution in the pipette and in the bath (Cl− pipette/ Cl− bath). When Cl− was replaced by HCO 3 − in the bath (Cl−/HCO 3 − ) the conductance of the channel at negative clamp voltages was reduced significantly by 40% for HT29 (n=6), 39% for T84 (n=7), and 38% for REC (n=6). Similarly, the zero-current potential (VI=0) was shifted from 0 mV (Cl−/Cl−) to negative values (Cl−/ HCO 3 − ) revealing permeability ratios $${{P_{{\text{Cl}}} } \mathord{\left/ {\vphantom {{P_{{\text{Cl}}} } {P_{{\text{H}}_{{\text{CO}}_{\text{3}} } } }}} \right. \kern-\nulldelimiterspace} {P_{{\text{H}}_{{\text{CO}}_{\text{3}} } } }}$$ of 2.4±0.1 for HT29 (n=6), 2.0±0.1 for T84 (n=7), and 1.8±0.1 for REC (n=7). With NaHCO3 as the pipette solution and NaCl in the bath, the VI=0 was positive and a $${{P_{{\text{Cl}}} } \mathord{\left/ {\vphantom {{P_{{\text{Cl}}} } {P_{{\text{H}}_{{\text{CO}}_{\text{3}} } } }}} \right. \kern-\nulldelimiterspace} {P_{{\text{H}}_{{\text{CO}}_{\text{3}} } } }}$$ , value of 2.3±0.1 was determined for HT29 (n=5). Replacement of Cl− in the bath by HCO 3 − reduced V I=0 to values close to 0 mV. In another series of experiments, the pipette was filled with 145 mmol/l NaCl and the bath contained 35 mmol/l NaCl to which 35 mmol/l NaHCO3 were added. We found that neither the conductance for the inward current nor VI=0 was changed significantly with the additon of NaHCO3 (HT29, n=6). We conclude that the HCO 3 − permeability and HCO 3 − conductance of these channels is about half of that for Cl−.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00372960
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