cAMP and calcium in generation of slow waves in cat colon

Rhythmic oscillations in interactions between cAMP and calcium have been proposed to account for a variety of rhythmic phenomena in cells. This idea was investigated in relation to the rhythmic signals (electrical slow waves) found in the electromyogram of the cat colon. A longitudinal strip of muscularis propria from cat colon was studied in a superfusion bath that allowed recording of the electromyogram from eight sites that were 2 cm apart. The effect of increasing cAMP (by exposure of the tissue to cAMP, dibutyryl cAMP, isobutylmethylxanthine, theophylline, caffeine, and papaverine) was to reduce frequency and amplitude of slow waves and duration of migrating spike bursts. All these maneuvers raised tissue cAMP levels. Dibutyryl cGMP and cGMP had no effect. THe changes in slow waves, but not migrating spike bursts, seen with raised cAMP levels were partly reversed by raising the calcium concentration in the extracellular fluid. Raising the extracellular sodium and potassium concentrations had no effect. The results are consistent with the hypothesis that interactions between cAMP and calcium are involved in slow-wave generation in colon muscle.