Insulin improves cardiomyocyte contractile function through enhancement of SERCA2a activity in simulated ischemia/reperfusion.
OBJECTIVE
Insulin exerts anti-apoptotic effects in both cardiomyocytes and coronary endothelial cells following ischemia/reperfusion (I/R) via the Akt-endothelial nitric oxide synthase survival signal pathway. This important insulin signaling might further contribute to the improvement of cardiac function after reperfusion. In this study, we tested the hypothesis that sarcoplasmic reticulum calcium-ATPase (SERCA2a) is involved in the insulin-induced improvement of cardiac contractile function following I/R.


METHODS
Ventricular myocytes were enzymatically isolated from adult SD rats. Simulated I/R was induced by perfusing cells with chemical anoxic solution for 15 min followed by reperfusion with Tyrode's solution with or without insulin for 30 min. Myocyte shortening and intracellular calcium transients were assessed and underlying mechanisms were investigated.


RESULTS
Reperfusion with insulin (10(-7) mol/L) significantly improved the recovery of contractile function (n=15-20 myocytes from 6-8 hearts, P<0.05), and increased calcium transients, as evidenced by the increased calcium [Ca2+] fluorescence ratio, shortened time to peak Ca2+ and time to 50% diastolic Ca2+, compared with those in cells reperfused with vehicle (P<0.05). In addition, Akt phosphorylation and SERCA2a activity were both increased in insulin-treated I/R cardiomyocytes, which were markedly inhibited by pretreatment of cells with a specific Akt inhibitor. Moreover, inhibition of Akt activity abolished insulin-induced positive contractile and calcium transients responses in I/R cardiomyocytes.


CONCLUSIONS
These data demonstrated for the first time that insulin improves the recovery of contractile function in simulated I/R cardiomyocytes in an Akt-dependent and SERCA2a-mediated fashion.
Yu
Jie
J
Department of Physiology, Xijing Hospital, Fourth Military Medical University, Xi' an 710032, China.
Zhang
Hai-feng
HF
Wu
Feng
F
Li
Qiu-xia
QX
Ma
Heng
H
Guo
Wen-yi
WY
Wang
Hai-chang
HC
Gao
Feng
F
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002469:Cell Separation; D006352:Heart Ventricles; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D015428:Myocardial Reperfusion Injury / Q000378:metabolism / Q000503:physiopathology; D032383:Myocytes, Cardiac / Q000378:metabolism*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism*; D015398:Signal Transduction
D007328:Insulin; C494918:AKT1 protein, human; D051057:Proto-Oncogene Proteins c-akt; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium