Editing Cardiac action potential (section)

==Gap junctions==
[[Gap junction]]s allow the action potential to be transferred from one cell to the next (they are said to ''electrically couple'' neighbouring [[cardiac myocytes|cardiac cells]]). They are made from the [[Connexin|connexin family]] of proteins, that form a pore through which ions (including Na<sup>+</sup>, Ca<sup>2+</sup> and K<sup>+</sup>) can pass. As potassium is highest within the cell, it is mainly potassium that passes through. This increased potassium in the neighbour cell causes the membrane potential to increase slightly, activating the sodium channels and initiating an action potential in this cell. (A brief chemical gradient driven efflux of Na+ through the [[connexon]] at peak depolarization causes the conduction of cell to cell depolarization, not potassium.)<ref>{{Cite book |last=Dubin |title=Ion Adventure in the Heartland Volume 1 |publisher=Cover Publishing Company |year=2003 |isbn=978-0-912912-11-0 |pages=145}}</ref> These connections allow for the rapid conduction of the action potential throughout the heart and are responsible for allowing all of the cells in the atria to contract together as well as all of the cells in the ventricles.<ref>{{Cite journal |last=Goodenough |first=Daniel A. |last2=Paul |first2=David L. |date=2009-07-01 |title=Gap junctions |journal=Cold Spring Harbor Perspectives in Biology |volume=1 |issue=1 |pages=a002576 |doi=10.1101/cshperspect.a002576 |issn=1943-0264 |pmc=2742079 |pmid=20066080}}</ref> Uncoordinated contraction of heart muscles is the basis for arrhythmia and heart failure.<ref>{{Cite journal |last=Severs |first=Nicholas J. |date=2002-12-01 |title=Gap junction remodeling in heart failure |journal=Journal of Cardiac Failure |volume=8 |issue=6 Suppl |pages=S293–299 |doi=10.1054/jcaf.2002.129255 |issn=1071-9164 |pmid=12555135}}</ref>