Fig. 2. Extracellular Ca²⁺ is not involved in RA-induced synaptic facilitation. The culture medium was replaced with Ca²⁺-free Ringer's solution (A) or Cd²⁺ was added to block the Ca²⁺ channels (B), 1015 minutes prior to the experiment. Short arrows marks the application of RA. Scale bars: 1 nA, 20 seconds, and 1 nA, 50 milliseconds for slow and fast traces, respectively. (C) Summary of the effects of RA on SSC frequency in normal culture medium, Ca²⁺-free medium and in medium containing Cd²⁺ (n=8-17). *P<0.05 compared with the control group (Student's t-test).