Figure 2. KCl- but not GABA-induced and spontaneous [Ca²⁺]_i increases in mature cultured midbrain neurons at DIV 31.

A, GABA applications (G, 50 μm) failed to induce Ca²⁺ transients while KCl (K20, 20 mm) induced responses with similar properties to those shown in Fig. 1. Responses were recorded in the presence of 0.3 μm TTX and 20 μm DNQX. Washout of TTX and DNQX (*) resulted in small spontaneous rises in [Ca²⁺]_i in all cells. Blockade of GABA_A receptors by bicuculline (Bic, 20 μm) led to synchronized Ca²⁺ oscillations with higher frequency and amplitudes than those at DIV 12 (Fig. 1). Ca²⁺ oscillations were reversibly blocked by DNQX (20 μm). B, average of the 10 traces shown in the top panel. Ca²⁺ transients were recorded in solutions buffered with HCO₃⁻. Inset shows fluorescence image of Fura-2-AM-loaded neurons from this experiment excited at 357 nm; scale bar, 50 μm.