Modulation by GABA(B) and delta opioid receptors of neurally induced responses in isolated guinea-pig taenia coli and human colonic circular muscle

Éva Makó, András Z. Rónai, György Ádám, Gábor Juhász, László Ritter, Béla Lestár, Vincenzo Crunelli

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Abstract

The GABA-ergic and opioid modulation of neurally induced muscle responses was studied in isolated guinea-pig taenia coli and human colonic circular muscle, using identical field stimulation parameters (rectangular pulses of 0.5 ms duration, 9 V·cm-1 intensity, trains of 3 pulses at 0.5 Hz, repeated every 1/3/5 min). The stimulation-induced contractions were inhibited in both preparations by GABA and baclofen; the IC50 values in human colonic circular muscle were ~ 100 and 31.0 μM, respectively. In guinea-pig taenia coli, the inhibition by 10-4 M GABA was dose-dependently reversed by 10-4-10-3 M of GABA(B) receptor antagonist CGP 35348; antagonism by phaclofen was less effective in the same concentration range. In human colonic circular muscle inhibition by 3 x 10-5 M baclofen was fully reversed by 10-3 M CGP 35348. With the exception of caecum, the delta 2 opioid receptor agonist deltorphin II was a potent inhibitor in human colonic circular muscle. 10-8 M Deltorphin caused a 74.4 ± 9.6% (n = 4) inhibition which was reversed by 10-6 M of delta receptor selective peptide antagonist BOC-Tyr-Pro-Gly-Phe-Leu-Thr(O(t)Bu). Deltorphin II was ineffective in guinea-pig taenia coli even at 10-6 M; the same concentration caused an 84.3 ± 7.9 (n = 4) inhibition in human preparations. It is concluded that: 1) GABA-ergic modulatory mechanisms are present both in human colonic circular muscle and guinea-pig taenia coli; 2) the GABA receptors involved are of type B; and 3) delta opioid receptor-mediated modulation functions only in human colonic circular muscle in regions other than the caecum. (C) 2000 Elsevier Science Ltd.

Original languageEnglish
Pages (from-to)135-138
Number of pages4
JournalJournal of Physiology Paris
Volume94
Issue number2
DOIs
Publication statusPublished - Mar 2000

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Keywords

  • Delta opioid receptors
  • GABA(B) receptors
  • Guinea-pig taenia coli
  • Human colonic circular muscle

ASJC Scopus subject areas

  • Neuroscience(all)
  • Physiology (medical)

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