EFFECTS OF Li-SUBSTITUTION ON HIGH-K INDUCED ONTRACTIONS OF VARIOUS SMOOTH MUSCLE TISSUES IN THE GUINEA-PIG

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The effects of partial Li-substitution for external Na in the medium on contraction, cellular Li concentration, and <SUP>45</SUP>Ca uptake of various smooth muscle tissues depolarized by a high-K (62.7 mM) solution were studied. In the taenia coli and ileum isolated from the guinea-pig, Li-substitution (23.7 mM-59.4 mM) increased the cellular Li concentration and strongly inhibited the K-contraction. A good correlation between cellular Li concentration and inhibition of tension was obtained in both the taenia coli and ileum. In the portal vein and uterus, Li-substitution inhibited K-contraction in correlation with Li-accumulation, although the inhibitory effect was weaker than those obtained with the taenia coli and ileum. In the aorta, Li-substitution did not affect K-contraction in spite of the accumulation of Li. The inhibitory effects of Li-substitution in all the tissues except the aorta were antagonized by an increase in external Ca, and the inhibition was accompanied by a decrease in cellular <SUP>45</SUP>Ca content. Although there is a tissue-specific defference, a possibility exists that excess cellular Li inhibits the K-induced Ca influx. The K-induced Ca influx in the aorta seems to be almost insensitive to the inhibitory effect of cellular Li.
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