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Type: Artigo de periódico
Title: Novel effects of guanidine on the neuromuscular junction
Author: RodriguesSimioni, L
SilvaCarvalho, I
Heluany, NF
Leite, GB
PradoFranceschi, J
CruzHofling, MA
Ballejo, G
Corrado, AP
Abstract: 1. The effects of guanidine on the isolated mouse phrenic nerve diaphragm(MPND) and chick biventer cervicis (CBC) neuromuscular preparations were determined by myographic and electrophysiological methods. 2. Guanidine at concentrations of 5-10 mM induced an initial facilitation followed by neuromuscular blockade in both preparations. In the isolated MPND such blockade was associated with the abolition of miniature end-plate potentials (MEPPs), but in the CBC the acetylcholine-induced contracture remained unimpaired. After guanidine removal, a heretofore undescribed pronounced facilitation of neuromuscular transmission associated with an increase in MEPP frequency was observed. Simultaneously, the muscular contractions exhibited delayed relaxation and aftercontractions. 3. The K+ channel opener, cromakalim (100-200 mu M) inhibited both the well-described initial and the novel postremoval facilitatory effects of guanidine in a concentration-dependent manner. These findings are consistent with the proposal that guanidine blocks K+ channels in motor nerve endings. 4. The guanidine-induced NMB was reverted by increasing the Ca2+ concentration (1.8-5 mM) in the nutritive solution. 5. Tetrodotoxin (TTX, 1.56 mu M) did not influence the increase in MEPPS frequency induced by guanidine (10 mM) but did reduce the rise in MEPPS frequency observed after guanidine removal. 6. The present findings indicate that the effects of guanidine on the neuromuscular junction are more complex than currently described because they include a neuromuscular blockade and a postremoval facilitation previously unreported in the literature. (C) 1997 Elsevier Science Inc.
Subject: guanidine
neuromuscular junction
postremoval facilitation
neuromuscular blockade
Country: Inglaterra
Editor: Pergamon-elsevier Science Ltd
Citation: General Pharmacology. Pergamon-elsevier Science Ltd, v. 28, n. 4, n. 599, n. 605, 1997.
Rights: fechado
Identifier DOI: 10.1016/S0306-3623(96)00229-7
Date Issue: 1997
Appears in Collections:Unicamp - Artigos e Outros Documentos

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