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 mu M. 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). IC(50)s were 0.84 and 226 mu M, 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 mu M). 5 Gd3+ antagonized VSOR Cl- current mon potently than La3+. The IC50 for Gd3+ was 23 mu M. In contrast, 100 mu M 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 mu M) and DIDS (10 mu M) inhibited L-type Ca2+ current 87 +/- 7 and 31 +/- 5%, respectively. Additionally, in the presence of 300 nM charybdotoxin, tamoxifen (1 mu M) and BIDS (10 mu M) inhibited delayed rectifier K+ current 38 +/- 8 and 10 +/- 2%, respectively. 7 The pharmacology of VSOR Cl- channels overlaps with voltage-dependent cation channels. BIDS 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.