Fig. 5.
Catecholamine challenge with ISO caused premature SCR in Trdn−/− myocytes and ventricular ectopy in Trdn−/− mice. (A) Representative examples of premature SCR (*) in a Trdn−/− myocyte during exposure to 1 μM ISO. Myocytes were loaded with Fura2 AM and paced at 1 Hz (vertical lines). (B) Average rate of SCRs during a 20-s recording period. Note that Ca2+ channel block with nifedipine (NIF, 20 μM) abolished the differences between the groups. Trdn+/+ (+/+): n = 39 (CON), 37 (ISO), and 61 (ISO + NIF); Trdn−/− (−/−): n = 46 (CON), 33 (ISO), and 67 (ISO + NIF); *, P < 0.001, Mann-Whitney test. (C) ECG records showing representative examples of ventricular extrasystoles (VES, #) and an episode of nonsustained ventricular tachycardia (VT) in conscious Trdn−/− mice after i.p. injection of ISO (1.5 mg/kg). (D) Average rate of VES and VT during a 1.5-h period after ISO challenge. *, P < 0.05, Mann-Whitney test. n = 8 mice per group.