While studies of gap junctions often cite their fundamental importance to normal electrical activation of the heart, there is little agreement on the degree of gap junction remodeling required to slow electrical activation. Our prior work has made the following seminal observations. First, the degree of cardiac hydration can modulate whether gap junction uncoupling will be associated with measurable conduction slowing and increased arrhythmia risk. Second, the microdomain adjacent to gap junction plaques is rich in the cardiac sodium channel isoform Nav1.5, is nominally 150 nm long and 10-20 nm wide. Through the use of super- resolution microscopy, electron microscopy, optical mapping, and cutting edge computations simulations, we provided evidence that the perinexus is a strong candidate structure as the cardiac ephapse. Third, we demonstrate that the buffer used to perform ex vivo whole-heart studies can modulate both perinexal width and the relationship between cardiac conduction and gap junctions. In short, altering extracellular sodium and potassium can compensate for a 50% loss of connexin43 such that conduction appears normal. These findings are entirely consistent with the various groups that have analyzed the relationship between conduction velocity and gap junctions, so much so that it is possible by post-hoc literature analysis to determine whether a group will find conduction slowing secondary to loss of Cx43 simply by the buffer used. This work is not just important for understanding alternative modes of electrical communication, but it points out an even more sobering issue: the foundational tool of ex vivo and in vitro biology (buffers) may yield investigator dependent results simply based on ionic buffer composition. In this application we will test three new aims. 1. We will test unique computational predictions of gap junctional and ephaptic coupling to demonstrate that the conduction reserve hypothesis is unique to continuous ?cable-like? propagation, and ephaptic coupling can self-attenuate conduction when intercellular widths are very narrow. 2. We will demonstrate how changing interfibrillar and perinexal separation separately alters cardiac conduction. These findings will be compared to models of ephaptic coupling in order to further support the hypothesis that ephaptic coupling is an alternative form of electrical coupling between myocytes. 3. We provide evidence that altering perfusate ion concentration can rescue conduction to the same degree as gap junction based therapy during acidosis. In this final aim, we will determine how perfusate composition modulates electrical coupling during no-flow ischemia and complete coronary artery ligation. Also, we will test whether perfusate composition can agonize the effects of gap junction therapy during ischemia.

Public Health Relevance

While studies often justify gap junction studies by citing their fundamental importance to normal electrical activation of the heart, there is little agreement on the degree of gap junction remodeling required to slow electrical activation. Our previous work suggested that an alternative form of electrical coupling operates in parallel with gap junction coupling and can compensate for the loss of gap junction coupling. This renewal will determine whether loss of gap junctions during the most common cardiac disease state (ischemia) can be recovered by preserving an alternative form of electrical coupling.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL102298-07
Application #
9402114
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Balijepalli, Ravi C
Project Start
2011-01-01
Project End
2020-11-30
Budget Start
2017-12-01
Budget End
2018-11-30
Support Year
7
Fiscal Year
2018
Total Cost
Indirect Cost
Name
Virginia Polytechnic Institute and State University
Department
Type
Organized Research Units
DUNS #
003137015
City
Blacksburg
State
VA
Country
United States
Zip Code
24061
Greer-Short, Amara; George, Sharon A; Poelzing, Steven et al. (2017) Revealing the Concealed Nature of Long-QT Type 3 Syndrome. Circ Arrhythm Electrophysiol 10:e004400
Entz 2nd, Michael; King, D Ryan; Poelzing, Steven (2017) Design and validation of a tissue bath 3-D printed with PLA for optically mapping suspended whole heart preparations. Am J Physiol Heart Circ Physiol 313:H1190-H1198
Hoeker, Gregory S; Skarsfeldt, Mark A; Jespersen, Thomas et al. (2017) Electrophysiologic effects of the IK1 inhibitor PA-6 are modulated by extracellular potassium in isolated guinea pig hearts. Physiol Rep 5:
Veeraraghavan, Rengasayee; Lin, Joyce; Keener, James P et al. (2016) Potassium channels in the Cx43 gap junction perinexus modulate ephaptic coupling: an experimental and modeling study. Pflugers Arch 468:1651-61
Abdullah, Osama M; Gomez, Arnold David; Merchant, Samer et al. (2016) Orientation dependence of microcirculation-induced diffusion signal in anisotropic tissues. Magn Reson Med 76:1252-62
George, Sharon A; Poelzing, Steven (2016) Cardiac conduction in isolated hearts of genetically modified mice--Connexin43 and salts. Prog Biophys Mol Biol 120:189-98
George, Sharon A; Sciuto, Katherine J; Lin, Joyce et al. (2015) Extracellular sodium and potassium levels modulate cardiac conduction in mice heterozygous null for the Connexin43 gene. Pflugers Arch 467:2287-97
Veeraraghavan, Rengasayee; Lin, Joyce; Hoeker, Gregory S et al. (2015) Sodium channels in the Cx43 gap junction perinexus may constitute a cardiac ephapse: an experimental and modeling study. Pflugers Arch 467:2093-105
Veeraraghavan, Rengasayee; Poelzing, Steven; Gourdie, Robert G (2014) Old cogs, new tricks: a scaffolding role for connexin43 and a junctional role for sodium channels? FEBS Lett 588:1244-8
Veeraraghavan, Rengasayee; Poelzing, Steven; Gourdie, Robert G (2014) Intercellular electrical communication in the heart: a new, active role for the intercalated disk. Cell Commun Adhes 21:161-7

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