Identification and regulation of K+ and Cl- channels in human parotid acinar cells.
The properties of K+ channels in these cells were studied using patch-clamp methods. Two channels, with conductances of 165+/-13 pS (n=6) and 30+/-1 pS (n=3), were identified in single-channel experiments. In cell-attached patches the reversal potentials were -67+/-8 and -74+/-2 mV for the large and small conductance channel, respectively, suggesting that both channels are K+-selective. The large conductance channel was also shown to be K+-selective in inside-out patches. The open probability (P(o)) of this channel was increased at depolarizing potentials and by increasing intracellular Ca2+ concentration ([Ca2+]i). These properties suggest that the large conductance channel is a 'maxi' Ca2+-activated K+ channel (BK(Ca)). The small conductance channel was not observed in inside-out patches. Carbachol (CCh; 10(-5) M) activated the BK(Ca) channel, but not the small conductance channel, in cell-attached patches. CCh also caused a dose-dependent increase in [Ca2+]i measured by fura-2 in microspectrofluorimetric studies, with a half-maximal response at approximately 3x10(-6) M. Neither isoproterenol (10(-5) M) nor substance P (10(-6) M) affected K+-channel activity or [Ca2+]i. In whole-cell experiments, CCh caused an increase in outward current. Charybdotoxin (10(-7) M), a BK(Ca) blocker, inhibited a large component of the CCh-induced current. A large component of the charybdotoxin-insensitive current may be carried by Ca2+-activated Cl- channels, which were also observed in human parotid acinar cells. The results indicate that BK(Ca) channels make a significant contribution to the whole-cell conductance in human parotid acinar cells.
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School of Biological Sciences, University of Manchester, G.38 Stopford Building, M13 9PT, Manchester, UK.
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Brown
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D000328:Adult; D000368:Aged; D002118:Calcium / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology; D065101:Chloride Channel Agonists; D018118:Chloride Channels / Q000032:analysis / Q000378:metabolism*; D018679:Cholinergic Agonists / Q000494:pharmacology; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008564:Membrane Potentials; D008875:Middle Aged; D010306:Parotid Gland / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000819:agonists* / Q000032:analysis / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
D065101:Chloride Channel Agonists; D018118:Chloride Channels; D018679:Cholinergic Agonists; D015221:Potassium Channels; D002217:Carbachol; D002118:Calcium