Fig 2. Effects of tetrodotoxin on I_Na,late in human atrial myocytes from patients in sinus rhythm (SR, black) and atrial fibrillation (AF, red) 50 ms and 250 ms after Na⁺ channel activation.

A Examples of original current tracings (top) measured at room temperature with protocol Ⅰ, under control conditions and in the presence of 10 μM TTX. Late sodium currents were measured 50 ms (left side) 250 ms (right side) after the beginning of the pulse at -30 mV (black arrow). B: Current density plotted for each voltage yielded a straight line after addition of TTX. C: Effect of 10 μM TTX on currents expressed as current density (in pA/pF) at -30 mV in SR and AF cardiomyocytes, and *P < 0.05, ***P < 0.001; paired Student’s t-test (B, C) for currents before and after exposure to TTX, or unpaired Student‘s t test with Welch’s correction for TTX-sensitive current in SR and AF.