Expression of skeletal muscle sodium channel (Nav1.4) or connexin32 prevents reperfusion arrhythmias in murine heart.
OBJECTIVE
acute myocardial ischaemia induces a decrease in resting membrane potential [which leads to reduction of action potential (AP) V(max)] and intracellular acidification (which closes gap junctions). Both contribute to conduction slowing. We hypothesized that ventricular expression of the skeletal muscle Na(+) channel, Nav1.4 (which activates fully at low membrane potentials), or connexin32 (Cx32, which is less pH-sensitive than connexin43) would support conduction and be antiarrhythmic. We tested this hypothesis in a murine model of ischaemia and reperfusion arrhythmias.


RESULTS
empty adenovirus (Sham) or adenoviral constructs expressing either SkM1 (gene encoding Nav1.4) or Cx32 genes were injected into the left ventricular wall. Four days later, ventricular tachycardia (VT) occurred during reperfusion following a 5 min coronary occlusion. In Nav1.4- and Cx32-expressing mice, VT incidence and duration were lower than in Sham (P < 0.05). In vitro multisite microelectrode mapping was performed in the superfused right ventricular wall. To simulate ischaemic conditions, [K(+)] in solution was increased to 10 mmol/L and/or pH was decreased to 6.0. Western blots revealed Cx32 and Nav1.4 expression in both ventricles. Nav1.4 APs showed higher V(max) and conduction velocity (CV) than Shams at normal and elevated [K(+)]. Exposure of tissue to acid solution reduced intracellular pH to 6.4. There was no difference in CV between Sham and Cx32 groups in control solution. Acid solution slowed CV in Sham (P < 0.05) but not in Cx32.


CONCLUSIONS
Nav1.4 or Cx32 expression preserved normal conduction in murine hearts and decreased the incidence of reperfusion VT.
Anyukhovsky
Evgeny P
EP
Department of Pharmacology, Center for Molecular Therapeutics, College of Physicians and Surgeons of Columbia University, 630 West 168 Street, PH 7West-318, New York, NY 10032, USA. ea29@columbia.edu
Sosunov
Eugene A
EA
Kryukova
Yelena N
YN
Prestia
Kevin
K
Ozgen
Nazira
N
Rivaud
Mathilde
M
Cohen
Ira S
IS
Robinson
Richard B
RB
Rosen
Michael R
MR
D000818:Animals; D001145:Arrhythmias, Cardiac / Q000235:genetics / Q000503:physiopathology / Q000517:prevention & control*; D017630:Connexins / Q000235:genetics* / Q000502:physiology*; D004195:Disease Models, Animal; D004562:Electrocardiography; D015870:Gene Expression; D006329:Heart Conduction System / Q000503:physiopathology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009124:Muscle Proteins / Q000235:genetics* / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D015428:Myocardial Reperfusion Injury / Q000235:genetics / Q000503:physiopathology / Q000517:prevention & control*; D011188:Potassium / Q000378:metabolism; D051381:Rats; D015222:Sodium Channels / Q000235:genetics* / Q000502:physiology*; D017180:Tachycardia, Ventricular / Q000235:genetics / Q000503:physiopathology / Q000517:prevention & control; D000097002:Gap Junction beta-1 Protein
D017630:Connexins; D009124:Muscle Proteins; D011188:Potassium; D015222:Sodium Channels; D000097002:Gap Junction beta-1 Protein; C466180:Scn4a protein, rat
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