Figure 8.

Bilirubin-induced enhancement in Ca²⁺ integrals through P/Q-type VGCC by pseudo AP trains. Example recordings of calcium currents in response to 50 Hz and 200 Hz AP like voltage ramps (AP waveform: −80 to + 40 mV, rise time: 2 ms, decay time: 6 ms; Top traces in a and b) in the presence of Ca²⁺ buffer EGTA at low concentration (0.5 mM) in pipette solution. The control solution was applied for 5 min, followed by the bath application of 6 μM bilirubin for 6 min and 500 nM ω- Agatoxin IVA for another 5 min. The paired pulse ratio of the amplitude of the second and the first spike at 50 Hz, 100 Hz, 200 Hz and 400 Hz in the absence (c, black circle) and presence of 6 μM bilirubin (c, red circle) described the difference in the facilitation of VGCCs. The area integral of calcium current evoked by AP trains increased at 50 Hz (d, red bar), 100 Hz (d, green bar), 200 Hz (d, cyan bar) and 400 Hz (d, magenta bar), and was all attenuated after applying ω- Agatoxin IVA (d, blue bars). *P < 0.05, **P < 0.01, ns, not significant, one-way ANOVA followed by Bonferroni post hoc test.