Effect of 4-aminopyridine on neurotransmission in smooth muscle
Papasova, M.; Bonev, A.; Boev, K.; Zafirov, D.; Gachilova, S.
Agressologie 23(3): 99-103
1982
ISSN/ISBN: 0002-1148 PMID: 6295199 Document Number: 192553
4-Aminopyridine (4-AP) exerted different effects on smooth-muscle strips isolated from the lower esophageal sphinter (LES), fundus (F) and antrum (A) of the stomach and the main pulmonary artery of the cat. In 29 of 37 fundic strips of 4-AP produced depolarization and contraction and in the remaining strips it led to relaxation. The contraction amplitude reached a maximum at concentrations of 5.104-8.104 M. After atropine (5.106 M) 4-AP caused relaxation instead of contraction. Phentolamine (5.106 M) and propranolol (5.106 M) partly suppressed the relaxation while tetrodotoxin (TTX) (3.107 M) abolished it. In the antral strips 4-AP (105-104 M) induced maximum hyperpolarization, decreased both amplitude and duration of the 2nd component of the slow potential and suppressed the spontaneous phasic contractions. The inhibitory effect of 4-AP much decreased after atropine, phentolamine and propranolol and was not observed at all after TTX. In the LES strips 4-AP (104 M) led to relaxation which increased after atropine, decreased after phentolamine and propranolol and did not occur after TTX. In helical strips from the main pulmonary artery 4-AP (105-5.104 M) elicited slow tonic contraction which was almost completely abolished by the combined application of atropine, phentolamine and propranolol. 4-AP may play a modulating role of adrenergic, cholinergic and non-adrenergic, non-cholinergic (purinergic) inhibitory nerve transmission.