Effects of TTX on APs of SANs in the control and HF groups. (A) Representative APs of control SANs at baseline, after treatment with 0.01% acetic acid and under TTX (1, 3 and 10 µM) infusion. (B) Average SAN beating rates, APA, MDP and DDR at baseline, after treatment with 0.01% acetic acid and under a TTX (1, 3 and 10 µM) infusion in the control group (n=6). (C) Representative APs of HF SANs at baseline, after treatment with 0.01% acetic acid and under TTX (1, 3 and 10 µM) infusion. (D) Average SAN beating rates, APA, MDP and DDR at baseline, after treatment with 0.01% acetic acid and under a TTX (1, 3 and 10 µM) infusion in the HF group (n=6). (E) AP block of SANs at baseline, after treatment with 0.01% acetic acid and under TTX (1, 3 and 10 µM) infusion in HF rabbits (n=6). AP block was defined as an AP with incomplete morphology and a lower amplitude compared that at baseline during the steady-state recording. *P<0.05, ***P<0.005 vs. baseline. AP, action potential; APA, AP amplitude; HF, heart failure; SAN, sinoatrial node; MDP, maximum diastolic potential; DDR, diastolic depolarization rate; TTX, tetrodotoxin.