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

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It was reported that the contractions in taenia coli induced by carbachol (1), ACh (2), phosphatidic acid (3) and high-potassium (K) (1, 4, 5) are all dependent on external calcium. On the other hand, Yukisada and Ebashi (6) have reported that rat, guinea pig, and rabbit ileum and rat uterus respond to barium (Ba) in the absence of external calcium. These results have been supported by experiments with rat uterus (7). In the first series of experiments in this paper, the relationship between Ba-induced tension development and external calcium was re-examined using isolated taenia coli preparations. K-induced contracture in taenia coli was reported to be composed of two phases, namely, phasic and tonic responses (5, 8). Furthermore, the tonic response was abolished in the presence of various inhibitors of metabolism and active transport (8). The second series of experiments were designed to examine the effect of the above mentioned inhibitors on Ba-induced tension development. Some of the results have already been reported (9).