Abstract 19997: Contrasting Regulatory Functions of Coronary Arterial Kvβ Subunits in Metabolic Hyperemia
Introduction: Sustained heart function requires high fidelity coupling between myocardial O2 consumption and coronary blood flow. Metabolic cues trigger hyperpolarization and relaxation of coronary vascular smooth muscle (CVSM) via voltage-gated K+ (KV) channels containing KV1.5 pore-forming subunits, yet molecular transducers linking O2 demand to CVSM excitability are unknown.
Hypothesis: CVSM redox status may alter KV1 function via ancillary β subunits, which bind pyridine nucleotides to modulate gating in excitable cells. In this study, we identified KVβ isoforms in CVSM and tested the hypothesis that KV1.5-associated β subunits modulate coronary vasodilation and myocardial flow during periods of increased O2 demand.
Methods: Presence of KVβ1, KVβ2 and KVβ3 transcript and protein was assessed in freshly-isolated murine left anterior descending (LAD) coronary arteries by qPCR and Western blot, respectively. KV1.5/β1/β2/β3 protein interactions were quantified by in situ proximity ligation assays. Contrast echocardiography was used to examine the relationship between cardiac work (mean arterial pressure x heart rate) and myocardial flow in wild type (wt), KVβ1.1-/-, and KVβ2Y90F (point mutant which eliminates KVβ2 oxidoreductase activity) animals during norepinephrine-induced cardiac work.
Results: Transcripts encoding KVβ1 and KVβ2 and corresponding proteins were detected in LAD coronary artery homogenates, whereas KVβ3 proteins were undetected. Molecular interaction between KV1.5/β1, KV1.5/β2 and KVβ1/β2 were detected at significantly higher levels in coronary arterial myocytes from wt vs. KVβ1.1-/- and KVβ2-/- (p<0.01), suggesting that KV1.5 channels associate with KVβ1.1/β2 heteromers in the coronary vasculature. The blood flow-cardiac work relationship was significantly enhanced in KVβ1.1-/-, but blunted in KVβ2Y90F mice animals compared with that in wt (p<0.05; n = 4 per group) animals, suggesting a dichotomous regulatory role for each of these subunits in coronary metabolic hyperemia.
Conclusions: In conclusion, findings suggest that KV1.5 in CVSM associates with KVβ1.1 and KVβ2 subunits, which differentially modulate channel function to fine tune metabolic hyperemia.
Author Disclosures: M.A. Nystoriak: None. V. Ohanyan: None. W.M. Chilian: None. A. Bhatnagar: None.
- © 2016 by American Heart Association, Inc.