Electrical activity in adenohypophyseal cells and effects of hypophyseotropic substances

Normal endocrine cells isolated from adenohypophyses of the rat, lizard, and fish, and maintained in short-term culture, produce action potentials spontaneously or in response to depolarizing current pulses or stimulant hypophyseotropic substances. Thyrotropin-releasing hormone elicited action potentials in a fraction of a mixed population of rat pars distalis cells. Dopamine, which inhibits basal secretion from rat melanotrophs and teleostean prolactin cells, inhibited action potential discharge in both these cell types. 5-Hydroxytryptamine, which stimulates secretion from lizard pars intermedia cells, stimulated action potentials in these cells. gamma-Aminobutyric acid, recently found in nerves to the rat pars intermedia and shown to have both stimulant and inhibitory effects on secretion, depolarized rat melanotrophs. The effect involved an increase in Cl conductance, which could be blocked by bicuculline and potentiated by diazepam. A Ca component that indicates inward Ca flux was present in the action potentials in each of the cell types examined, although its contribution varied with species and gland region. Electrical activity may therefore participate in secretory control in adenohypophyseal cells. Attention is drawn to some unexpected electrical responses to agents that are likely to be used in attempts to examine the correlation between the electrical events and secretion.