Figure 6. Ca²⁺-dependent intracellular acidification.

(A) Simultaneous monitoring of pH_i and E_gly with respect to 8-sec of simple spiking (red) and complex spiking (black) in one cell. Arrowheads indicate glycine (2 mM) responses. The pH-sensitive dye SNARF-5F's signal is the average fluorescence intensity of a region of interest drawn inside the cell body. An intracellular acidification, manifest as a decrease in SNARF's signal, occurred during both simple spiking and complex spiking. Black bar above SNARF traces indicate the duration of 8-sec depolarizing current injection. (B) The intracellular acidification was also seen with Ca²⁺ spiking (in TTX) and inhibited by zero-Ca²⁺ (replaced with Co²⁺ or Mg²⁺) or 300 μM Cd²⁺. (Bi-ii) Simultaneously recorded SNARF signal and E_gly from two cells. The 8-sec depolarizing current injections evoking Ca²⁺ spikes or just depolarization after Ca²⁺ channel block are marked with thick bars above SNARF traces. The amount of injected current is shown beside each symbol along with the number of evoked Ca²⁺ spikes in parenthesis. An example of complete block (Bi) and incomplete block (Bii) of the depolarization-induced acidification by zero-Ca²⁺ is shown. (Biii) Relation between the change in SNARF signal to the peak negative E_gly shift in control condition and the peak positive E_gly shift in Ca²⁺ block condition for 8 cells. (C) The change in pH_i and [Ca²⁺]_i induced by 8-sec complex spiking were detected by simultaneous 2-photon imaging of SNARF-5F and Fluo-4 or Fura-2. Examples from 2 different cells are shown. The duration of 8-sec depolarizing current injection evoking complex spikes is indicated by the shaded rectangle. The excitation wavelengths were 800 nm (Ci) and 780 nm (Cii).