GABA output neurons in substantia nigra display spontaneous hyperpolarizations (SHPs) or spontaneous miniature outward currents (SMOCs) that are generated by the activation of small conductance, calcium activated potassium channels (SK channels) through ryanodine receptor-mediated calcium release from intracellular stores. To study their involvement in spontaneous discharge we used 1-EBIO that increases the calcium sensitivity of SK channels. Gramicidin perforated patch recording revealed that 1-EBIO (200 mM) strongly increased the duration of SMOCs, but not their frequency. The duration of afterhyperpolarizations (AHP) following each action potential also strongly increased. Discharge was affected in two ways: The increase in AHP duration reduced discharge frequency. Despite its low frequency, discharge became more regular. Silent periods interspersed with intermittent discharge lasted longer in 1-EBIO because of the increased duration of SMOC induced SHPs. SHPs were occluded by AHPs, hence, the effect of SMOCs on discharge depended on the duration of AHPs on the one hand and SMOC frequency on the other. Therefore, activation of ryanodine receptors inhibited spontaneous discharge only if interspike intervals were longer than AHP duration. In addition, prolonged SHPs reduced spike threshold. We conclude that SHPs facilitate the transition between continuous and intermittent discharge -Supported by the DFG-