Effects of caffeine on the electrical and mechanical properties of the smooth muscle of various regions of the guinea pig alimentary canal were investigated.
1) Caffeine (5mM) produced contracture (caffeine contracture) in the circular muscle of the stomach and the longitudinal muscle of the ileum, jejunum, caecum (taenia coli), and rectum. In the presence of caffeine, regular phasic contraction ceased in the stomach and taenia coli, but increased in the ileum, jejunum, and rectum.
2) Caffeine (5mM) eliminated the generation of the tonic response completely and suppressed the phasic response of K-induced contracture recorded from all regions of the alimentary canal.
3)Caffeine (5mM) suppressed the spike and slow wave which were generated in the stomach, without any change of the membrane potential and membrane resistance.
4) In Na-free (tris), Ca-free, and Cl-deficient (NO₃) solutions, generation of the slow wave recorded from the stomach was suppressed and in Cl-deficient (Br) solution, the frequency of the slow wave was increased. However, caffeine (5mM) produced contracture in all the above solutions without any marked change of the membrane potential and resistance.
5) Caffeine (5mM) depolarized the membrane in the ileum, taenia, and rectum and enhanced the spike amplitude and frequency in the ileum and rectum. However, it decreased the membrane resistance in the taenia coli and rectum, but increased or did not change the membrane resistance in the ileum.
6) ATP (5mM) and theophylline (5mM) suppressed the generation of the slow wave recorded from the stomach. Theophylline induced contracture, but the amplitude was smaller than that induced by caffeine (5mM). ATP did not induce contracture.
7) From the above results, the effects of caffeine are discussed in relation to the topical differences of the membrane properties in the alimentary canal. The roles of Ca in relation to actions of caffeine on the electrical and mechanical properties are also discussed.