OCT3 gated intracellular β1AR activation enhances excitation‐contraction coupling in heart

Abstract

Rationaleβ1AR‐adrenergic receptor (β1AR) plays a central role in sympathetic regulation of cardiac excitation‐contraction (EC) coupling. Stimulation of β1AR by catecholamines enhances cardiomyocyte contraction and Ca2+transient via the cAMP‐protein kinase A (PKA) pathway. Organic cation transporter 3 (OCT3) plays a role in cleaning up the extracellular catecholamines and transporting a portion of catecholamine into myocardium. Recent progress found that β1AR is also present at intracellular membranes. However, how the intracellular β1AR was activated, and the role of OCT3 in regulating intracellular β1AR signaling and EC‐coupling remains unknown.ObjectiveTo characterize the presence and activation of intracellular β1AR‐adrenergic receptors and their impact on cardiac EC‐couplingMethods and ResultsWe used a genetic deletion of OCT3 to inhibit the entrance of catecholamine into the cells. We used isolated myocytes to measure β1AR‐induced contractility and Ca2+transients. We used PKA activity reporters to detect local activation via intracellular β1AR. We found that catecholamine‐induced inotropic effects were diminished in OCT3‐knock out hearts. OCT3 deficiency significantly attenuated norepinephrine (NE) induced PKA activities at the sarcoplasmic reticulum, myocyte contractility, and Ca2+transient. Additional data show β1AR associates with sarco/endoplasmic reticulum Ca2+‐ATPase (SERCA) at the sarcoplasmic reticulum (SR). Inhibition of OCT3 blocked the transportation of NE, and attenuated β1AR‐induced PKA activity at the SR and EC‐coupling.ConclusionOur finding demonstrates a previously unrecognized intracellular β1AR‐mediated local PKA activity at SR that is gated by OCT3. Upon catecholamine stimulation, this SR‐localized β1AR signal plays a critical role in promoting E‐C coupling and cardiac contractile function. Thus, internal β1AR signaling may presents a novel therapeutic target in cardiac diseases treatment.Support or Funding InformationNIH HL113413VABX009200