Heart failure modulates electropharmacological characteristics of sinoatrial nodes

Abstract

The impact of heart failure (HF) on sinoatrial node (SAN) channel regulation and electropharmacological responses has remained elusive. The present study aimed to investigate the effects of HF on the electrical activity of SANs with and without pharmacological interventions. Action potentials (APs) were recorded in isolated SANs from normal rabbits (control) and those with HF (rapid ventricular pacing for 4 weeks) prior to and after administration of a funny current blocker (ivabradine; 0.1, 0.3, 3 or 10 µM), a calmodulin kinase II inhibitor (KN-93; 0.3 or 3 µM), a sarcoplasmic reticulum Ca²⁺ release inhibitor (ryanodine; 0.3 or 3 µM), a sodium current inhibitor (tetrodotoxin; 1, 3 or 10 µM) and a late sodium current inhibitor (ranolazine; 10 µM). Western blot analysis was used to investigate the protein expression in SANs from normal rabbits and those with HF. Control SANs had a higher beating rate than SANs from rabbits with HF (2.3±0.1 vs. 1.5±0.1 Hz; P<0.001). Similarly, ivabradine (10 µM), KN-93 (3 µM), ranolazine (10 µM) and ryanodine (3 µM) decreased the beating rates of SANs in the control (n=6) and HF (n=6) groups. Ivabradine treatment resulted in a higher incidence of AP block in HF vs. control SANs (66.7 vs. 0%; P<0.05). Tetrodotoxin (1, 3 or 10 µM) decreased the beating rate to a higher extent in SANs from rabbits with HF than in those from control rabbits and induced a higher incidence of AP block (66.7 vs. 0%; P<0.05). Furthermore, SANs from rabbits with HF had higher protein levels of phospholamban (PLB) and lower levels of hyperpolarization-activated cyclic nucleotide-gated potassium channel 4, ryanodine receptor and phosphorylated PLB than control SANs. In conclusion, HF modulates electropharmacological responses in the SAN by channel regulation, which may result in SAN dysfunction.

Keywords: KN-93; heart failure; ivabradine; ranolazine; ryanodine; tetrodotoxin.

Figure 1.

Effects of ivabradine on APs of SANs in the control and HF groups. Panel (A) Representative APs of control SANs prior to and after treatment with ivabradine (0.1, 0.3, 3 and 10 µM). (B) Average SAN beating rates, APA, MDP and DDR prior to and after treatment with ivabradine (0.1, 0.3, 3 and 10 µM) in the control group (n=6). (C) Representative APs of HF SANs prior to and after treatment with ivabradine (0.1, 0.3, 3 and 10 µM). (D) Average SAN beating rates, APA, MDP and DDR prior to and after treatment with ivabradine (0.1, 0.3, 3 and 10 µM) in the HF group (n=6). (E) Representative APs and incidence of ivabradine-induced AP block in HF SANs. 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 (0.03% dimethyl sulfoxide). AP, action potential; APA, AP amplitude; HF, heart failure; SAN, sinoatrial node; MDP, maximum diastolic potential; DDR, diastolic depolarization rate.

Figure 2.

Effects of KN-93 on APs of SANs in the control and HF groups. (A) Representative APs of control SANs prior to and after treatment with KN-93 (0.3 and 3 µM). (B) Average SAN beating rates, APA, MDP and DDR prior to and after treatment with KN-93 (0.3 and 3 µM) in the control group (n=6). (C) Representative APs of HF SANs prior to and after treatment with KN-93 (0.3 and 3 µM). (D) Average SAN beating rates, APA, MDP and DDR prior to and after treatment with KN-93 (0.3 and 3 µM) in the HF group (n=6). *P<0.05 vs. baseline (0.03% dimethyl sulfoxide). AP, action potential; APA, AP amplitude; HF, heart failure; SAN, sinoatrial node; MDP, maximum diastolic potential; DDR, diastolic depolarization rate.

Figure 3.

Effects of ryanodine and Ran on APs of SANs in the control and HF groups. (A) Representative APs of control SANs prior to and after treatment with ryanodine (0.3 and 3 µM). (B) Average SAN beating rates, APA, MDP and DDR prior to and after treatment with ryanodine (0.3 and 3 µM) in the control group (n=6). (C) Representative APs of HF SANs prior to and after treatment with ryanodine (0.3 and 3 µM). (D) Average SAN beating rates, APA, MDP and DDR prior to and after treatment with ryanodine (0.3 and 3 µM) in the HF group (n=6). (E) Representative APs of control SANs prior to and after treatment with Ran (10 µM). (F) Average SAN beating rates, APA, MDP and DDR prior to and after treatment with Ran (10 µM) infusion in the control group (n=6). (G) Representative APs of HF SANs prior to and after treatment with Ran (10 µM). (H) Average SAN beating rates, APA, MDP and DDR prior to and after treatment with Ran (10 µM) in the HF group (n=6). *P<0.05 vs. baseline (0.03% dimethyl sulfoxide) of ryanodine. AP, action potential; APA, AP amplitude; HF, heart failure; SAN, sinoatrial node; MDP, maximum diastolic potential; DDR, diastolic depolarization rate; Ran, ranolazine.

Figure 4.

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.

Figure 5.

Protein expression of HCN4, CaMKII, SERCA2a, phospholamban (PLB), PLB-T17, RyR and Nav1.5 in sinoatrial nodes from control rabbits and those with HF (n=6 per group) was analyzed by western blot analysis. α-Sarcomeric actin was used as a loading control. *P<0.05, **P<0.01 vs. control. HF, heart failure; HCN4, hyperpolarization-activated cyclic nucleotide-gated potassium channel 4; CaMKII, calmodulin kinase II; SERCA2a, sarcoplasmic reticulum Ca²⁺-ATPase; PLB, phospholamban; PLB-T17, phosphorylated PLB; Ryr, ryanodine receptor; Nav1.5, sodium channel, voltage-gated, type V.