Calcium ions and the post-tetanic hyperpolarization of bullfrog sympathetic ganglion cells.

1. Tetraethylammonium (TEA) augmented the amplitude of the later phase of the post-tetanic hyperpolarization (PTH) in bullfrog sympathetic ganglion cells. The present report deals with the mechanism underlying the later phase (the late slow component )of PTH. 2. The late slow component persisted in the presence of ouabain, suggesting that it was not associated with the activation of the Na pump. 3. The membrane conductance was increased during the development of the late slow component. The polarity of the late slow component was reversed when the conditioning hyperpolarization exceeded the potassium equilibrium potential. 4. The amplitude of the late slow component was increased in the potassium-free solution and decreased in the potassium-rich solution, and was not affected by replacing external chloride ions with methylsulfate ions. 5. The late slow component was abolished in the low-calcium solution or in the solution containing manganese ions, whereas it was augmented in the calcium-rich solution. 6. These results suggest that the late slow component is produced by an increase in potassium conductance of the cell membrane, which is caused by an increase in the calcium influx during the generation of action potentials.