Shimizu, K., Hori, M., Mitsui, M., Hayashi, Y., Nakajyo, S. and Urakawa, N. The properties of a high K⁺-induced contraction in the ileal longitudinal and circular muscles of cat. Japanese Journal of Smooth Muscle Research 1987, 23 (1), 47-53. Hypertonic 60 mM KC1 (H 60K⁺) solution induced a phasic contraction followed by tonic one in the longitudinal (long.) and circular (circ.) muscles of cat ileum. Verapamil inhibited the tonic contraction in the long. or circ. muscle with IC₅₀ of 2.0×10^-8 M or 1.0×10^-7 M, respectively. The sensitivity of the long. muscle to verapamil was higher than that of the circ. muscle. Ouabain (10^-5 M) increased or did not change the tonic contraction, and increased intracellular Na+ contents in the long. and circ. muscles in H 60K+ solution. Li⁺-substituted (1/5-1/2) solutions decreased the H 60K⁺-induced contraction in the long. muscle, but potentiated or did not change the contraction in the circ. one. The results with glucose removal, hypoxia, DNP application and a measurement of oxygen consumption showed that the H 60K⁺-induced contractions in the long. and circ. muscles are probably dependent on aerobic metabolism utilizing external glucose as well as endogenous substrates. In summary, properties of the H 60K⁺-induced contraction in the ileal long. of cat was not entirely similar to those of circ. muscles, but they were different from those of the ileal of other animal species and had some similarities to those of the guinea-pig portal vein.