SPONTANEOUS ACTIVITY AND RELATED CALCIUM MOVEMENTS OF FISH INTESTINAL SMOOTH-MUSCLE - EFFECT OF DEPOLARIZATION, CAFFEINE AND LANTHANUM

1. 1. Flounder intestinal smooth muscle possessed a slow spontaneous contractile rhythm. Both KCl and caffeine induced contractures in the preparation. 2. 2. In both Ca-free EGTA media and in La3+ salines both spontaneous activity and KCl responses were abolished. 3. 3. Fine structural studies revealed a large extracellular matrix but only a scanty sub-membrane vesicle development. This was mirrored in the Ca4 5 efflux curve which possessed a large fast component and a small slow component. 4. 4. KCl and La3+ simulated fibre Ca4 5 efflux but caffeine was without such effect. At the same time tissue Ca4 5 uptake was increased by caffeine, reduced by KCl and strongly reduced by La3+ 5. 5. Tension development in this muscle appears strongly dependent upon an influx of extracellular calcium and intracellular calcium fluxes may play only a minor role in the overall calcium utilization during contraction. © 1979.