Fig. 3.

Serotonin is not released via exocytosis. Representative amperometric current traces measured using carbon-fiber amperometry with a miniature amperometric electrode polarized at +600 mV. (A) Amperometric traces of pinealocytes preloaded with exogenous dopamine. Enlarged single quantal events in the Right are from the numbered spikes from the Left (1: spontaneous event, 2, 3: evoked exocytosis). The three amperometric spikes illustrated correspond to 2-electron oxidation of 1.7 × 10⁷, 2.1 × 10⁷, and 270 × 10⁷ dopamine molecules, respectively. In the remaining panels, pinealocytes were not preloaded with dopamine. The amperometric electrode was placed in the bath solution without pinealocytes (control traces) (B and D) or on a cluster of pinealocytes (C and E). ACh (50 μM) and high potassium chloride (70 mM KCl) were used to elicit membrane depolarization and intracellular Ca²⁺ increases. Next, 1 μM NE (an oxidizable molecule) was applied to the electrode in the bath (D) or with the same electrode touching pinealocytes (E). No quantal events were observed before or after NE application, only a step up of current as applied NE is being oxidized.