Sprint training shortens prolonged action potential duration in postinfarction rat myocyte: mechanisms.
Two electrophysiological manifestations of myocardial infarction (MI)-induced myocyte hypertrophy are prolongation of action potential duration (APD) and reduction of transient outward current (I(to)) density. Because high-intensity sprint training (HIST) ameliorated myocyte hypertrophy and improved myocyte Ca(2+) homeostasis and contractility after MI, the present study evaluated whether 6-8 wk of HIST would shorten the prolonged APD and improve the depressed I(to) in post-MI myocytes. There were no differences in resting membrane potential and action potential amplitude (APA) measured in myocytes isolated from sham-sedentary (Sed), MI-Sed, and MI-HIST groups. Times required for repolarization to 50 and 90% APA were significantly (P < 0.001) prolonged in MI-Sed myocytes. HIST reduced times required for repolarization to 50 and 90% APA to values observed in Sham-Sed myocytes. The fast and slow components of I(to) were significantly (P < 0.0001) reduced in MI-Sed myocytes. HIST significantly (P < 0.001) enhanced the fast and slow components of I(to) in MI myocytes, although not to levels observed in Sham-Sed myocytes. There were no significant differences in steady-state I(to) inactivation and activation parameters among Sham-Sed, MI-Sed, and MI-HIST myocytes. Likewise, recovery from time-dependent inactivation was also similar among the three groups. We suggest that normalization of APD after MI by HIST may be mediated by restoration of I(to) toward normal levels.
Zhang
X Q
XQ
Weis Center for Research, Geisinger Medical Center, Danville, PA 17822, USA.
Zhang
L Q
LQ
Palmer
B M
BM
Ng
Y C
YC
Musch
T I
TI
Moore
R L
RL
Cheung
J Y
JY
D000200:Action Potentials; D000818:Animals; D002478:Cells, Cultured; D006321:Heart / Q000502:physiology / Q000503:physiopathology*; D006346:Heart Septum / Q000502:physiology / Q000503:physiopathology; D006352:Heart Ventricles; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D009203:Myocardial Infarction / Q000473:pathology / Q000503:physiopathology*; D009206:Myocardium / Q000166:cytology / Q000473:pathology; D018408:Patch-Clamp Techniques; D010805:Physical Conditioning, Animal / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D012420:Running / Q000502:physiology*