Characterization of the calcium-activated chloride channel in isolated guinea-pig hepatocytes.
Macroscopic and unitary currents through Ca(2+)-activated Cl- channels were examined in enzymatically isolated guinea-pig hepatocytes using whole-cell, excised outside-out and inside-out configurations of the patch-clamp technique. When K+ conductances were blocked and the intracellular Ca2+ concentration ([Ca2+]i) was set at 1 microM (pCa = 6), membrane currents were observed under whole-cell voltage-clamp conditions. The reversal potential of the current shifted by approximately 60 mV per 10-fold change in the external Cl- concentration. In addition, the current did not appear when Cl- was omitted from the internal and external solutions, indicating that the current was Cl- selective. The current was activated by increasing [Ca2+]i and was inactivated in Ca(2+)-free, 5 mM EGTA internal solution (pCa > 9). The current was inhibited by bath application of 9-anthracenecarboxylic acid (9-AC) and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) in a voltage-dependent manner. In single channel recordings from outside-out patches, unitary current activity was observed, whose averaged slope conductance was 7.4 +/- 0.5 pS (n = 18). The single channel activity responded to extracellular Cl- changes as expected for a Cl- channel current. The open time distribution was best described by a single exponential function with mean open lifetime of 97.6 +/- 10.4 ms (n = 11), while at least two exponentials were required to fit the closed time distributions with a time constant for the fast component of 21.5 +/- 2.8 ms (n = 11) and that for the slow component of 411.9 +/- 52.0 ms (n = 11). In excised inside-out patch recordings, channel open probability was sensitive to [Ca2+]i. The relationship between [Ca2+]i and channel activity was fitted by the Hill equation with a Hill coefficient of 3.4 and the half-maximal activation was 0.48 microM. These results suggest that guinea-pig hepatocytes possess Ca(2+)-activated Cl- channels.
Koumi
S
S
First Department of Internal Medicine, Nippon Medical School, Tokyo, Japan.
Sato
R
R
Aramaki
T
T
D000465:Algorithms; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D018118:Chloride Channels / Q000378:metabolism*; D004594:Electrophysiology; D005260:Female; D006168:Guinea Pigs; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques
D018118:Chloride Channels; D002118:Calcium