The influence of calcium on the electrical and mechanical activity of the guinea pig ureter.

Low calcium concentration in the external medium depolarises the membrane of smooth muscle cells of the ureter and their excitability diminishes. The Ca++ dependent oscillations of the action potential disappears, while the plateau component is more resistent. Analogous reactions are observed by the addition of Ca++ antagonists such as Lantanum or Verapramil. A high Calcium concentration produces a slight hyperpolarisation, which stabilises the membrane and enhances the spike component while decreasing the plateau component of the action potential. It is possible that several drugs act indirectly on the ureter by changing the relationship between the calcium concentration of the external versus the internal medium.