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

• Published in: Pflügers Archiv Vol. 419; no. 2; pp. 190 - 196
• Main Authors: GREGER, R, NITSCHKE, R. B, LOHRMANN, E, BURHOFF, I, HROPOT, M, ENGLERT, H. C, LANG, H. J
• Format: Conference Proceeding Journal Article
• Language: English
• Published: Heidelberg Springer 01-09-1991
• Subjects: Animals; Biological and medical sciences; Chloride Channels; Chlorides - metabolism; Colon - drug effects; Colon - metabolism; Digestive system; Female; Ion Channels - drug effects; Ion Channels - metabolism; Male; Medical sciences; Membrane Proteins - drug effects; Membrane Proteins - metabolism; Molecular Structure; Nitrobenzoates - chemistry; Nitrobenzoates - pharmacology; Pharmacology. Drug treatments; Rabbits; Gut; Diarrhea; Electrophysiology; Rabbit; Ionic channel; Lagomorpha; In vitro; Voiding dysfunction; Vertebrata; Mammalia; Animal; Chlorides; Digestive diseases; Inhibitor; Colon; Exocrine secretion
• ISSN: 0031-6768; 1432-2013
• DOI: 10.1007/BF00373006

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).