Figure 6. Effects of a depolarizing prepulse on CHA-induced I_Ca inhibition.

A, three consecutive current traces in response to 50 ms test pulses from V_h= -80 to -20 mV. The middle test pulse (P2) was preceded by a 5 ms prepulse to +150 mV for 100 ms. The three traces in each panel correspond to before (Control), during and after (Wash) application of 10⁻⁶ M CHA. Most of the CHA-induced I_Ca inhibition was reversed by a depolarizing prepulse. B, summary of the change in the facilitation ratio by CHA. I_Ca amplitude between 3 and 8 ms was averaged and the facilitation ratio was calculated by dividing the C₂ current amplitude by the corresponding C₁ current amplitude. The facilitation ratio (C₂/C₁) was significantly greater in the presence of CHA than without CHA (control, 1.22 ± 0.04; CHA, 1.75 ± 0.10; * P < 0.05).