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

✍ Scribed by R. Greger; R. B. Nitschke; E. Lohrmann; I. Burhoff; M. Hropot; H. C. Englert; H. J. Lang

• Book ID: 104746393
• Publisher: Springer
• Year: 1991
• Tongue: English
• Weight: 722 KB
• Volume: 419
• Category: Article
• ISSN: 0031-6768
• DOI: 10.1007/bf00373006

✦ Synopsis

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 = Vt~/ Rt~) was calculated. After serosal (s) and mucosal (m) addition of indomethacin (1 ~tmol/1) Isc was -71 _+ 11 (n = 118) gA/cm 1. Amiloride (0.1 mmol/1, m) inhibited this current and reversed the polarity to + 32 + 4 (n = 118) gA/cm 2. In the presence of amiloride and indomethacin, prostaglandin E 2 (l gmol/1, s), known to induce C1-secretion, generated an Isc of -143 + 8 (n = 92) I.tA/cm 2. The arylaminobenzoate and C1-channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) reduced Isc reversibly with a half-maximal inhibition (ICso) at approximately 0.35mmol/1 and 0.2 retool/1 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 ICs0 to approximately 0.1 mmol/1. 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 ICso to approximately 50 gmol/1. 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 C1conductance in the thick ascending limb of the loop of Henle (TAL). In the present study the (+) enantiomer inhibited significantly more strongly than the (-) form. This suggests that the inhibitory effect of NPPB, even though it requires rather high concentrations, is probably due to C1-channel inhibition. For other arylaminobenzoates the sequence of potencies was different from that determined for the TAL. The present data indicate that substances that have been designed to block * Supported by DFG Gr 480/10 Offprint requests to: R. Greger the C1-conductance of the TAL segment also inhibit reversibly but with much lower affinity the PGEz-induced C1-secretion in rabbit colon.