Mn2+ (5 mM) inhibited completely the K+ (60 mM)-induced ileal tonic tension to the base line, however, the tension increased progressively to the above level of the original K+ tonic response after 3 hr of the Mn2+ application at 37 degrees C. 2. At 30, 32 or 34 degrees C, the tensions which developed after 3 hr of the addition of 5 mM Mn2+ in the high-K+ medium was 0, 21, 48% of their original K+ tonic levels, respectively. 3. The tension development and manganese uptake in the presence of Mn2+ in the high-K+ medium was highly dependent on the temperature in very narrow range of 32-37 degrees C in the suspending medium.
