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  • Title: [Caffeine-induced contraction of guinea pig taenia coli (author's transl)].
    Author: Takahashi S, Chujyo N.
    Journal: Nihon Yakurigaku Zasshi; 1978 Jan; 74(1):61-75. PubMed ID: 640536.
    Abstract:
    Caffeine (10 or 20 mM)-induced isometric contraction of guinea pig taenia coli showed two successively occurring phasic contractions (I and II) followed by a low sustained tension. Half-time of tension decay in II was 4 approximately 6 times longer than in I. The contraction occasionally showed only a single phasic contraction, of which tension, however, decayed showing two half-times as in two phasic contractions. In the presence of procaine 0.1 approximately 0.5 mM, DNP 0.03 approximately 0.1 mM or Mn2+ 0.5 approximately 1.0 mM, II was entirely abolished whereas I was partially inhibited and such were confirmed by analyzing the time course of tension decay. Maximal tension of I decreased in parallel with lowering the external Na while II was enhanced with 50 approximately 100 mM Na and inhibited by further withdrawal of Na. I and II showed the same Ca-dependecy with respect to the inhibition by Ca deficiency and to the time course of recovery from Ca-free state. Refractoriness to caffeine after preceding caffeine-contraction also showed little difference between I and II. Sustained tension by caffeine was dependent on Ca in the same manner as tonic K-contracture. Increase in 45Ca uptake with 40 mM K was completely inhibited by 10 mM caffeine while cellular Ca content in the presence of high K markedly increased with caffeine indicating the decrease in Ca exchangeability. The above results indicate that caffeine induced contraction consists of two phasic contractions of which EC-coupling Ca is released from two different cellular sites, and that the phasic contractions are followed by a sustained low tension caused by an increased Ca influx. In the presence of high K, caffeine abolishes the increase in Ca influx by high K and sequesters the sarcoplasmic free Ca resulting in the relaxation of K-contracture.
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