The Effects And Mechanism Of Action Of Leptin On Contractile Function Of Adult Rat Cardiomyocyte

Background and Aim:Leptin, a16kDa hormone from the OB gene, has been identified as an importantprotein involved obesity. As a chronic metabolic disorder, Obesity is associated with ahigh risk of developing cardiovascular and metabolic diseases, such as heart failure. Themain aim of this paper is to probe the effects of leptin on contractile function ofcardiomyocyte in adult rat. And the mechanism of the action of leptin involved of calciumsensitivity, oxidative stress and autophagy were investigated.MethodsThe calcium transients and contraction in adult rat cardiomyocytes were recordedwith Spectral Fluorescence Detection System. The effects of1,10,100nM leptin oncalcium transient and contraction within30min were observed.After the incubation with leptin, the reactivity of cardiomyocyte to gradientconcentration calcium (1.8,2.4,3.6,5.4mM) was observed to detect the effects of leptinon calcium sensitivity.Using the corresponding agents such as apocynin, tempol and rapamycin, theunderlying mechanism of leptin involved of oxidative stress and autophagy wasdetermined. Werstern blotting was employed to evaluate the expression of p70S6K andphosphorylated proteins, PKCε, LC3B and Beclin1.Results(1) The peak of calcium transient were markedly decreased while perfusing thecardiomyocytes with1nM leptin (P<0.05). There was no significant difference in bl, TB50%and TP50%in1nM leptin group (P>0.05). All indexs including bl, peak, TB50%and TP50%significantly declined in10nM leptin group (P<0.05). And bl and peak ofcalcium transient significantly descended in cardiac myocytes treated with100nM leptin(P<0.05).(2) Within30min, the TPS50%and TR50%of myocyte length increased incardiomyocytes treated with1nM leptin (P<0.05). The PS and+dL/dtmaxsignificantlydeclined in10nM leptin group (P<0.05). And PS, TR50%and±dL/dtmaxsignificantlychanged in100nM leptin group (P<0.05).(3) Leptin could significantly reduce calcium sensitivity of ventricular myocyteswhich were perfused with1.8,2.4,3.6,5.4mM calcium (P<0.05). The PS and±dL/dtmaxrestrained and TR50%extended in leptin group (P<0.05).(4) Apocynin or tempol inhibited the decreasing of the calcium transient, myocytecontraction and the calcium sensitivity induced by leptin (P<0.05). Compared with CTLgroup, rapamycin has no significant effects on calcium transient and myocyte contraction(P>0.05). However, rapamycin could significantly block the effects of leptin on calciumtransient and myocyte contraction (P<0.05).(5) Leptin induced oxidative stress as evidenced by decreased LC3B and Beclin1levels and increased PKCε levels. The effects were obliterated by apocynin or tempol.Leptin restrained autophagy as evidenced by decreased LC3B and Beclin1levels andincreased p-p70S6K levels. The effects were obliterated by rapamycin.ConclusionLeptin has depressing effects on intracellular free calcium and myocardial systolicfunction, as well as decreasing calcium sensitivity. Apocynin, tempol or rapamycin couldblock the effects of leptin. The mechanism involved oxidative stress and autophagy.