Effects of anion channel antagonists in canine colonic myocytes: comparative pharmacology of Cl-, Ca2+ and K+ currents.
1. Volume-Sensitive, Outwardly Rectifying (VSOR) Cl- currents were measured in canine colonic myocytes by whole-cell patch clamp. Decreasing extracellular osmolarity 50 milliosmoles l-1 activated current that was carried by Cl- and 5 - 7 times greater in the outward direction. 2. Niflumic acid, an inhibitor of Ca2+-activated Cl- channels, did not inhibit VSOR Cl- current. Glibenclamide, an antagonist of CFTR, and anthracene-9-carboxylate (9-AC) inhibited current less than 25% at 100 microM. 3. DIDS (4, 4-diisothiocyanato-stilbene-2,2'disulphonate) inhibited VSOR Cl- current more potently than SITS (4-acetamido-4'-isothiocyanato-stilbene-2,2'-disulphonate). IC50s were 0.84 and 226 microM, respectively. 4. VSOR Cl- current was strongly inhibited by tamoxifen ([Z]-1-[p-dimethylaminoethoxy-phenyl]-1,2-diphenyl-1-butene), an anti-oestrogen compound (IC50=0.57 microM). 5. Gd3+ antagonized VSOR Cl- current more potently than La3+. The IC50 for Gd3+ was 23 microM. In contrast, 100 microM La3+ inhibited current only 35+/-7%. 6. Antagonists of VSOR Cl- current had non-specific effects. These compounds blocked voltage-dependent K+ and Ca2+ currents in colonic myocytes. Tamoxifen (10 microM) and DIDS (10 microM) inhibited L-type Ca2+ current 87+/-7 and 31+/-5%, respectively. Additionally, in the presence of 300 nM charybdotoxin, tamoxifen (1 microM) and DIDS (10 microM) inhibited delayed rectifier K+ current 38+/-8 and 10+/-2%, respectively. 7. The pharmacology of VSOR Cl- channels overlaps with voltage-dependent cation channels. DIDS and tamoxifen inhibited VSOR Cl- equally. However, because DIDS had much less effect on L-type Ca2+ and delayed rectifier K+ channels than did tamoxifen, it might be useful in experiments to investigate the physiological and pathophysiological role of this conductance in whole tissues.
Dick
G M
GM
Department of Physiology & Cell Biology, University of Nevada School of Medicine, Anderson Medical Building/352, Reno, Nevada, NV 89557, USA.
Kong
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ID
Sanders
K M
KM
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology*; D000818:Animals; D017920:Antiporters / Q000037:antagonists & inhibitors*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects*; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000187:drug effects*; D003106:Colon / Q000166:cytology / Q000187:drug effects*; D004285:Dogs; D005260:Female; D007038:Hypotonic Solutions / Q000494:pharmacology; D007552:Isotonic Solutions / Q000494:pharmacology; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000187:drug effects*
D017920:Antiporters; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D018118:Chloride Channels; D007038:Hypotonic Solutions; D007552:Isotonic Solutions; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid