An analysis of 5-HT hyperpolarization of sympathetic ganglion cells

Bullfrog sympathetic ganglion cells treated with nicotine are hyperpolarized with application of 5-HT. This 5-HT hyperpolarization, however, was not observed if preparations were pretreated with d-TC before being treated with nicotine. When preparations were treated with ACh or carbamylcholine, which transiently depolarizes ganglion cells, hyperpolarization did take place. Such was also observed in the presence of Ringer's solution if preparations were pretreated with the K+-free Ringer's solution. These results suggested that ganglion cells were hyperpolarized by the action of 5-HT when the Na+-pump of these cells was accelerated by accumulation of intracellular Na+, as the result of a transient depolarization or extracellular K+ deficiency.