Plateau Formation in Action Potential of Guinea-Pig Ureter

1. Effects of changes in the external calcium cancentration on the electrical and mechanical activity in smooth muscle of ureter of guinea-pig have been studied by means of the sucrose-gap method and the mechano-electronic transducer. 2. Within a range of excess calium between 4.4mM to 6.6mM, the amplitude and the frequency of action potential were reduced. The membrane potential was increased slightly. 3. Within a range of excess calcium between 11mM to 44mM, the action potential was diminished and the membrane potential was increased slightly. 4. Total absebce of excess calcium in the external solution inhibited the generation of action potential initially and then theplateau type action potential reappeared. The oscillatory potentials developed on the later phase of plateau with the exposure time. 5. In excess potassium and calcium-free solution, the duration of plateau of action potential was shortened and the spike diminished finally. 6. In both potassium and calcium-free solution, the generation of action potential was inhibited transiently and then the action potentials reappeared. The duration of reappeared action potentials was not changed. 7. In both sodium and calcium-free solution, replaced by sucrose, lithium or choline, the plateau type action potential was abolished immediately.