[Caffeine-induced contraction of guinea pig taenia coli (author's transl)].
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.
D000818:Animals; D002110:Caffeine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D003106:Colon / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D008297:Male; D008345:Manganese / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D013696:Temperature; D013997:Time Factors
D002110:Caffeine; D008345:Manganese; D012964:Sodium; D011188:Potassium; D002118:Calcium