Potassium-induced relaxations of the guinea-pig taenia coli
Ishii, T.; Shimo, Y.
Archives Internationales de Pharmacodynamie et de Therapie 239(1): 36-44
1979
ISSN/ISBN: 0003-9780 PMID: 485718 Document Number: 152028
In the isolated tenia coli with myenteric plexus of the guinea-pig, excess K (5-60 mM) caused transient relaxations followed by contraction in Tyrode's solution. The amplitudes of relaxations elicited by low K (5-10 mM) were inversely related to K concentration, while those by high K (30-40 mM) were increased in dose-dependent manner. The maximum relaxation was obtained by the addition of 40 mM K. This relaxation amounted to .apprx. 51% of the control by isoprenaline (1 .times. 10-6 M). Ouabain (5 .times. 10-7 M) abolished the relaxation induced by 5 mM K but not the one induced by 40 mM K. Tetrodotoxin (5 .times. 10-7 M) abolished the 40 mM K-induced relaxation but not the 5 mM K-induced one. In tenia preparation free of myenteric plexus, high K concentration at 40 mM did not relax the tissue, but low K (5 mM) still caused the same type of relaxation as that seen in taenia preparation with myenteric plexus. Guanethidine (5 .times. 10-6 M), phentolamine (1 .times. 10-5 M) or propranolol (1 .times. 10-6 M) had no effect on either type of K-induced relaxations. Apparently 2 types of K-induced relaxation exist, one is due to an activation of an electrogenic Na pump of the smooth muscle membrane, the other is due to a stimulation of non-adrenergic inhibitory nerves in the myenteric plexus of the tenia.