Figure 1. Randomly occurring outward current pulses (OCPs) are generated by RyR-mediated Ca²⁺ release from intracellular stores in GABAergic SNr neurons.

A, cyclopiazonic acid (CPA, 10 μm) abolished OCPs within minutes. Traces shown were recorded at a holding potential of –60 mV and sampled for one minute in control condition (Aa) and in CPA (Ab). Calibration in Ab applies also to Aa. B and C, summary graphs illustrating normalized OCP frequency over 1 min, before and following application of apamin (0.3 μm, n = 5) and ryanodine (10 μm, n = 3). B, apamin, which blocks small-conductance Ca²⁺-activated potassium channels, abolished OCPs. C, ryanodine (10 μm), which blocks ryanodine receptors, abolished OCPs (n = 3). D, frequency and E, sum of area (s-area) enveloped by OCPs were increased by caffeine (1 mm) and by action potential discharge recorded for 1–3 min. The summed OCP area was also enhanced upon depolarization by 5 mV (from –60 to –55 mV, E). The number of cells (D, E) and s.e.m. (B,C,D,E) are indicated in this and all other figures if appropriate. Asterisks (*P < 0.05) indicate a significant increase over baseline levels in this and all other figures (dashed line at 1.0 on y axis).