title: Optogenetic release of norepinephrine from cardiac sympathetic neurons alters mechanical and electrical function.
abstract: OBJECTIVE
  Release of norepinephrine (NE) from sympathetic neurons enhances heart rate (HR) and developed force through activation of β-adrenergic receptors, and this sympathoexcitation is a key risk for the generation of cardiac arrhythmias. Studies of β-adrenergic modulation of cardiac function typically involve the administration of exogenous β-adrenergic receptor agonists to directly elicit global β-adrenergic receptor activation by bypassing the involvement of sympathetic nerve terminals. In this work, we use a novel method to activate sympathetic fibres within the myocardium of Langendorff-perfused hearts while measuring changes in electrical and mechanical function.
  
  
  RESULTS
  The light-activated optogenetic protein channelrhodopsin-2 (ChR2) was expressed in murine catecholaminergic sympathetic neurons. Sympathetic fibres were then photoactivated to examine changes in contractile force, HR, and cardiac electrical activity. Incidence of arrhythmia was measured with and without exposure to photoactivation of sympathetic fibres, and hearts were optically mapped to detect changes in action potential durations and conduction velocities. Results demonstrate facilitation of both developed force and HR after photostimulated release of NE, with increases in contractile force and HR of 34.5 ± 5.5 and 25.0 ± 9.3%, respectively. Photostimulation of sympathetic fibres also made hearts more susceptible to arrhythmia, with greater incidence and severity. In addition, optically mapped action potentials displayed a small but significant shortening of the plateau phase (-5.5 ± 1.0 ms) after photostimulation.
  
  
  CONCLUSIONS
  This study characterizes a powerful and clinically relevant new model for studies of cardiac arrhythmias generated by increasing the activity of sympathetic nerve terminals and the resulting activation of myocyte β-adrenergic receptors.
authors.affiliation: Department of Biomedical Engineering, The George Washington University, Phillips Hall, Room 607, 801 22nd Street NW, Washington, DC 20052, USA.
authors.forename: Anastasia M
authors.initials: AM
authors.lastname: Wengrowski
authors.affiliation: Department of Pharmacology and Physiology, The George Washington University, Washington, DC, USA.
authors.forename: Xin
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Biomedical Engineering, The George Washington University, Phillips Hall, Room 607, 801 22nd Street NW, Washington, DC 20052, USA.
authors.forename: Srinivas
authors.initials: S
authors.lastname: Tapa
authors.affiliation: Department of Pharmacology and Physiology, The George Washington University, Washington, DC, USA.
authors.forename: Nikki Gillum
authors.initials: NG
authors.lastname: Posnack
authors.affiliation: Department of Pharmacology and Physiology, The George Washington University, Washington, DC, USA.
authors.forename: David
authors.initials: D
authors.lastname: Mendelowitz
authors.affiliation: Department of Biomedical Engineering, The George Washington University, Phillips Hall, Room 607, 801 22nd Street NW, Washington, DC 20052, USA Department of Pharmacology and Physiology, The George Washington University, Washington, DC, USA kaymwk@gmail.com.
authors.forename: Matthew W
authors.initials: MW
authors.lastname: Kay
mesh_terms: D000818:Animals; D004558:Electric Stimulation / Q000379:methods; D006321:Heart / Q000502:physiology; D006329:Heart Conduction System / Q000378:metabolism / Q000503:physiopathology; D006339:Heart Rate / Q000502:physiology; D051379:Mice; D009206:Myocardium / Q000378:metabolism; D009474:Neurons / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism*; D062308:Optogenetics / Q000379:methods; D011943:Receptors, Adrenergic, beta / Q000378:metabolism; D013564:Sympathetic Nervous System / Q000378:metabolism* / Q000503:physiopathology
chemical_list: D011943:Receptors, Adrenergic, beta; D009638:Norepinephrine
keywords: Arrhythmia; Langendorff; Optogenetic; Sympathetic activation