Fig. 3. Time-dependent properties of I_Na in atrial and ventricular myocytes of the rainbow trout heart. (A) Development of rested-state inactivation of I_Na. Increased duration of the prepulse at -80 mV reduces I_Na elicited by the test pulse to -20 mV for 30 ms. (B) Recovery of I_Na from inactivation (reactivation). The amplitude of I_Na elicited by test pulses to -20 mV for 100 ms increases as a function of the time interval between the prepulse P₁ and the test pulse P₂. Voltage protocols of I_Na are shown at the top, representative recordings in the middle and mean (± s.e.m.) results from 9-14 myocytes at the bottom. Asterisks show a significant difference (P<0.05) between atrial and ventricular myocytes.