Abstract 14577: Kvβ1.1 Binds Pyridine Nucleotides and Alters Cardiac Action Potential

Abstract

Introduction: Kvβ1 subunits demonstrate a unique ability to bind pyridine nucleotides and alter Kv channel function. Pyridine nucleotide levels are altered in cardiovascular diseases resulting in higher NADH levels. Therefore coupling of the Kvβ1 subunit with Kv channels may be important in how the repolarization is modulated in presence of NADH. Hypothesis: The Kvβ1 subunits are highly expressed in the heart and bind to multiple Kv channels (Kv4.x and Kv1.x) and regulate Kv channel activity. Therefore, we evaluated pyridine nucleotide changes in cardiovascular disease in the presence and absence of Kvβ1 and how they modulate Kv channel activity. Methods: Wild type (WT) and Kvβ1 knockout (KO) mice hearts (n=7 each group) using the ex-vivo Langendorff system were exposed to both acute and chronic alterations of lactate to induce an increase in NADH levels. Cardiac monophasic action potentials (MAPs) were measured before and 10 min after perfusion of the lactate, for chronic alterations mice were injected with isoprenaline to induce cardiac hypertrophy and demonstrated significant NADH increase. In addition we performed pull-down assays to identify binding partners of Kvβ1.1 in the heart. Results: We observed that, lactate exposure (10mmole/L) ( p <0.05) prolonged left ventricular MAP duration in WT (9.4±0.7 vs. 15.6±1.2* at APD50) however KO mice demonstrated no significant difference (10.9±0.5 vs. 11.7±1.1). NADH levels in lactate exposed hearts demonstrated a 3 fold increase compared with control Krebs buffer. Lactate prolonged MAP durations in WT hearts, which was reversal by adding pyruvate (20mmole/L) to its control (pre-lactate; 8±0.5 vs. 13.6±0.6* vs. 8.4±0.6). The chronic model, MAP duration significantly ( p <0.01) prolonged in the WT (9.7±0.7 vs. 15.3±1.1*) mouse hearts after isoprenaline infusion but not KO mouse (12.4±1.8 vs. 14.4±1). Immunoprecipitation experiments indicate that Kvβ1.1 interacts with Kv4.2 and Kv1.5 from mouse heart. Conclusions: Results obtained from this study suggested that the Kvβ1.1 subunit has the ability to sense redox changes including NAD/NADH alterations and modulate MAP through Kv activity. This study highlights the physiological role Kvβ1.1 plays in cardiac repolarization physiology and cardiac disease.