Effects of arylaminobenzoate-type chloride channel blockers on equivalent short-circuit current in rabbit colon

Abstract

Arylaminobenzoates were examined in rabbit colon mounted in an Ussing chamber. The open-circuit transepithelial voltage (Vte) and resistance (Rte) were measured and the equivalent short-circuit current (Isc = Vte/Rte) was calculated. After serosal (s) and mucosal (m) addition of indomethacin (1 mumol/l) Isc was -71 +/- 11 (n = 118) microA/cm2. Amiloride (0.1 mmol/l, m) inhibited this current and reversed the polarity to +32 +/- 4 (n = 118) microA/cm2. In the presence of amiloride and indomethacin, prostaglandin E2 (1 mumol/l, s), known to induce Cl- secretion, generated an Isc of -143 +/- 8 (n = 92) microA/cm2. The arylaminobenzoate and Cl- channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) reduced Isc reversibly with a half-maximal inhibition (IC50) at approximately 0.35 mmol/l and 0.2 mmol/l for mucosal and serosal application respectively. To test whether the poor effect was caused by mucus covering the luminal surface, dose/response curves of the mucosal effect were repeated after several pretreatments. Acidic pH on the mucosal side reduced IC50 to approximately 0.1 mmol/l. A similar effect was observed after N-acetyl-L-cysteine (m) preincubation. Pretreatment with N-acetyl-L-cysteine (m) and carbachol (s), in order to exhaust mucus secretion, and L-homocysteine (m) were more effective and reduced IC50 to approximately 50 mumol/l. To test whether this effect of NPPB was caused by non-specific effects, the two enantiomers of 5-nitro-2-(+/-1-phenylethylamino)-benzoate were tested of which only the (+) form inhibited the Cl- conductance in the thick ascending limb of the loop of Henle (TAL).(ABSTRACT TRUNCATED AT 250 WORDS)

A Chromanol Type of K⁺ Channel Blocker Inhibits Forskolin- but Not Carbachol-Mediated Cl- Secretion in Rat and Rabbit Colon

“…In whole cell patch clamp studies in rat colonic crypt cells from the base, CCH hyperpolarized the membrane voltage (Vm) and enhanced whole cell conductance (Gm). In agreement with previous impalement studies, 10 qmol/1 293 B depolarized Vm in forskolin-treated rat colonic crypt base cells even further and reduced Gm. In Ussing cham ber experiments in rabbit colon, 293 B abolished the 1^ induced by PGE2.…”

“…Ussing chamber experiments were performed in rabbit distal colon as reported previously [1,10]. Rab bits of either sex (1.5-3 kg b.w.)…”

Regulatory volume decrease in a renal distal tubular cell line (A6) I. Role of K+ and Cl−

“…The former anion passes through most CI-channels but is not translocated by the KC1 cotransport system [2,4]. We found that the RVD was insensitive to the CI-channel blocker NPPB [14]. However, this compound does not block all C1-conductive pathways and different effects have been reported in the literature.…”

The distribution and expression of CFTR restricts electrogenic anion secretion to the ileum of the brushtail possum, Trichosurus vulpecula

“…The IC 50 values of both GlyH101 and NPPB were tenfold higher in the intact tissue when compared with their effect on cloned pCFTR expressed in FRT cells. However, similar discrepancies between the effect of these compounds in expression systems and native intestinal tissues have been reported for the eutherian intestine and are thought to result from diffusional barriers that limit the access of the inhibitors to the channel (Diener and Rummel, 1989;Greger et al, 1991). Given the location of CFTR at the base of the villi and in the crypts in the possum ileum, similar diffusional barriers are likely to occur in the possum.…”