Measurements of electrical activity and intracellular Ca<sup>2+</sup> levels were performed in perforated-patch clamped GH<sub>3</sub> cells to determine the contribution of large-conductance calcium-activated K<sup>+</sup> (BK) channels to action potential repolarization and size of the associated Ca<sup>2+</sup> oscillations. By examining the dependence of action potential (AP) duration on extracellular Ca<sup>2+</sup> levels in the presence and the absence of the specific BK channel blocker paxilline, it is observed that plateau-like action potentials are associated to low densities of paxilline-sensitive currents. Extracellular Ca<sup>2+</sup> increases or paxilline additions are not able to largely modify action potential duration in cells showing a reduced expression of BK currents. Furthermore, specific blockade of these currents with paxilline systematically elongates AP duration, but only under conditions in which short APs and/or prominent BK currents recorded under voltage-clamp mode are present in the same cells. Our data indicate that in GH<sub>3</sub> cells, BK channels act primarily ending the action potential and suggest that by contributing to fine-tuning cellular electrical properties and hence intracellular Ca<sup>2+</sup> variations, BK channels may play an important role on time- and cell-dependent modulation of physiological outputs in adenohypophyseal cells.