The Role of the Electrogenic Sodium Pump in Modulation of Pacemaker Discharge of 'Aplysia' Neurons

The discharge of Aplysia pacemaker neurons varies with temperature over the range of 10 to 22C. Three types of temperature-frequency plots are found, with maximal discharge at lowest, intermediate or highest temperatures. In the presence of ouabain, however, all cells show maximal discharge at the highest temperature, suggesting that the steady-state activity of an electrogenic sodium pump is an important determinant of membrane excitability. The average magnitude of pump current, as indicated by the applied current necessary to restore discharge to control values after ouabain application, was about 4nA at 20C but near zero at 10C. These neurons may be excellent models of mammalian thermoreceptors.