Evaluation of the stimulatory capacity of procaine on Na transport through frog skin.

Procaine has different effects on various ionic conductive pathways through the frog skin. We investigated the season and temperature dependence of the stimulation by mucosal procaine, of the Na-conductive pathway. For this stimulation, we found higher half-maximal saturation constants (KNa) in winter animals (6.38 +/- 0.8 mmol/l), than in summer ones (4.03 +/- 0.7 mmol/l). Summer frogs kept for 2 weeks at 4 degrees C, reacted like winter frogs (6.24 +/- 0.8 mmol/l). However, the maximal sodium currents (INa max) did not depend on temperature adaptation. Procaine-induced increased of KNa is associated with an increase of INa. The effects of procaine associated with BIG (benzoylimidazole-2-guanidine) were non-additive, while with vasopressin they were additive. A biphasic, dose-dependent response was recorded after procaine application to the inner surface. Vasopressin counteracted the serosal procaine-induced inhibition of the Na-transport.