EFFECTS OF EXTERNAL CALCIUM AND SOME METABOLIC INHIBITORS ON BARIUM-INDUCED TENSION CHANGES IN GUINEA PIG TAENIA COLI

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Abstract
0.01 0.1 mM Ba developed tension periodically and more than 0.5 mM induced tonic response in taenia coli. 0. 5 mM Ba had no effect on taenia coli when external Ca was removed. With" higher concentrations (20 mM) of Ba, a small part of the contracture was not dependent on external Ca though the greater part of Ba-induced tension development seems dependent on external Ca. Ba has little capacity to substitute for Ca in the development of K-induced tension in taenia coli. The existence of a nondepolarized membrane for Ba-induced tension development is suggested. Factors which abolish the K-induced tonic response also abolished the Ba-contracture. Anoxia, glucose removal and DNP (denitrophenol] (1 x 10-4 M) abolished the tonic response and Ba produced only a phasic response, similar to K-contracture. Li substitution and ouabain (2.5 x 10-6 M) abolished the Ba-contracture in a pattern different from K-contracture. Removal of external K from the medium abolished Ba-contracture similarly as with ouabain. Ba-induced tension development is generally dependent on external Ca; Ba-induced tension development was inhibited by some metabolic inhibitors; factors which inhibited the development of Ba-contracture were devided into 2 groups DNP type and ouabain type, according to the pattern of inhibition of the contracture.