Figure 3.

Effects of I_Na inhibition by tetrodotoxin (TTX), propafenone and lidocaine on SR Ca²⁺ release events. (A) 5 µM TTX applied via similar cross-over protocol to flecainide experiments induced a similar reduction in Ca²⁺ spark frequency (P = 0.009, n = 14 cells). (B) 5 µM TTX reduced wave frequency (P = 0.0002, n = 10 cells). (C) Wave velocity is significantly reduced in the presence of TTX (P = 0.012 by Student's t-test, NT: n = 84 waves; TTX: n = 34 waves from 10 cells). (D) Similar to flecainide experiments, no significant change in SR load was seen in the presence of 5 µM TTX (P = 0.97 by Student's t-test, n = 20 cells from three isolations). (E) 5 μM propafenone reduced Ca²⁺ wave frequency in a similar manner (P = 0.0007, n = 10 cells), as did (F) 200 μM lidocaine (P = 0.0012, n = 10 cells).