Electrophysiological consequences of acute regional ischemia/reperfusion in neonatal rat ventricular myocyte monolayers.
BACKGROUND
Electrophysiological changes promoting arrhythmias during acute regional ischemia/reperfusion are challenging to study in intact cardiac tissue because of complex 3-dimensional myocardial and vascular geometry. We characterized electrophysiological alterations and arrhythmias during regional ischemia/reperfusion in a simpler 2-dimensional geometry of cultured neonatal rat ventricular myocyte monolayers.


RESULTS
Optical mapping of intracellular Ca (Ca(i)) and voltage was performed with the use of Rhod 2-AM and Rh-237, respectively. Regional ischemia was mimicked by covering the central portion of monolayer with a glass coverslip, and reperfusion was mimicked by removing the coverslip. Monolayers were stained with fluorescent antibodies to detect total and dephosphorylated connexin-43 at various time points. During coverslip ischemia, action potential duration shortened, Ca(i) transient duration was prolonged, and local conduction velocity (CV) slowed progressively, with loss of excitability after 10.6 +/- 3.6 minutes. CV slowing was accompanied by connexin-43 dephosphorylation. During ischemia, spontaneous reentry occurred in 5 of 11 monolayers, initiated by extrasystoles arising from the border zone or unidirectional conduction block of paced beats. On reperfusion, excitability recovered within 1.0 +/- 0.8 minutes, but CV remained depressed for 9.0 +/- 3.0 minutes, promoting reentry in the reperfused zone. As connexin-43 phosphorylation recovered in the reperfused zone, CV normalized, and arrhythmias resolved.


CONCLUSIONS
Acute regional ischemia/reperfusion in neonatal rat ventricular myocyte monolayers recapitulates electrophysiological alterations and arrhythmias similar to those observed during acute coronary occlusion/reperfusion in intact hearts. During early reperfusion, slow recovery from connexin-43 dephosphorylation leads to persistent CV slowing, creating a highly arrhythmogenic substrate.
de Diego
Carlos
C
UCLA Cardiovascular Research Laboratory, Department of Medicine, Division of Cardiology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA.
Pai
Rakesh K
RK
Chen
Fuhua
F
Xie
Lai-Hua
LH
De Leeuw
Jan
J
Weiss
James N
JN
Valderrábano
Miguel
M
D000818:Animals; D000831:Animals, Newborn; D001145:Arrhythmias, Cardiac; D018031:Connexin 43 / Q000378:metabolism; D004594:Electrophysiology; D006352:Heart Ventricles / Q000473:pathology*; D008955:Models, Cardiovascular; D032342:Muscle Cells / Q000473:pathology*; D015428:Myocardial Reperfusion Injury / Q000503:physiopathology*; D010766:Phosphorylation; D051381:Rats
D018031:Connexin 43