Effects Of Visfatin On Ion Channels In Rat Cardiac Ventricular Myocytes

Visfatin is a proteinic cytokine secreted by fat tissue. Plasma visfatin concentrations correlate strongly with the amount of visceral fat, but only weakly with the amount of subcutaneous fat. Visfatin was identified previously as a pre–B cell colony-enhancing factor (PBEF), and its molecular weight was 52-kilodalton. Visfatin is secreted from the macrophage in the white fat tissue. Visfatin is not only highly expressed in visceral fat, but has a disparity of expression in the skeletal muscle, liver, bone marrow and lymphocytes. Visfatin exerts an insulin-mimetic effect, which is closely associated with metabolic and chronic inflammatory diseases. Recently, it was reported that visfatin could alleviate ischemia-reperfusion (I/R) injury. Many ion channels are correlated with I/R injury. It is generally accepted that Na+/Ca2+ exchanger inhibitors can exert a cardioprotective effect. In our study, isolated rat ventricular myocytes and whole cell patch clamp technique were used to identify the effect of visfatin on INa/Ca, ICa,L and IKATP in isolated rat ventricular myocytes in an attempt to clarify the ion channel mechanism of visfatin on the myocardium.ObjectiveThis study was to identify the effect of visfatin on ion channel current such as INa/Ca, ICa,L and IKATP in isolated rat ventricular myocytes, and clarify the ion channel mechanism of the cardioprotective effect of visfatin.MethodsMale SD rats (250-320g) were heparinized and then sacrificed by decapitation after being anesthetized. The heart was removed immediately, and the aorta of the isolated heart was connected to a Langendorff apparatus and perfused with Ca²⁺-free Tyrode's solution for 5 min at a rate of 10 ml/min, and then with the same solution containing collagenase I. After dissociation and collection,cells were mechanically dispersed and stored in KB solution at 4℃. The membrane current of the isolated rat ventricular myocytes was recorded by the whole cell patch clamp technique. INa/Ca, ICa,L and I_KATP of the myocytes perfused with or without visfatin were recorded and analyzed. Results1.Effects of visfatin on INa/Ca in isolated rat ventricular myocytesVisfatin increased both inward and outward INa/Ca in isolated rat ventricular myocytes. After 5-min perfusion with the extracellular fluid, the inward and outward sodium-calcium exchange current decreased by 5±5% and 2±7% respectively in the control group, while the inward sodium-calcium exchange current increased by 20±12% (n=6, P<0.05), 24±6% (n=6, P<0.05)and 35±5% after treatment with visfatin at a concentrations of 25 nmol/L, 250 nmol/L and 500 nmol/L respectively (n=5, P<0.05). Outward INa/Ca decreased by 2%±8% after perfusion with 25nmol/L visfatin(n=6, P>0.05), and increased by 6±4% and 15±3% after perfusion with 250 nmol/L and 500 nmol/L visfatin respectively (n=6, P<0.05; n=5, P<0.05).2. Effects of visfatin on ICa, L in isolated rat ventricular myocytesVisfatin inhibited ICa, L in rat ventricular myocytes. After perfusion with visfatin at the concentration of 250 nmol/L for 5 min, ICa, L decreased by 18±4% (n=6). ICa, L of the control group decreased by 4±5% (n=8) because of the phenomenon"rundown". There was a significant difference between the visfatin group and the control group (P<0.01).3. Effects of visfatin on I_KATP in isolated rat ventricular myocytesThe clamped membrane potential was -40 mV, and then a ramp pulse protocol of 125 ms from 50 mV to -100 mV was used to record the quasi-steady-state current (I_KATP). Pinacidil brought about a marked increase to the current, which was completely inhibited by glibenclamide, indicating that the outward current recorded was I_KATP. No change to I_KATP was observed after perfusion of 250 nmol/L visfatin for 5 min, indicating that visfatin could not open the KATP channel of cardiomyocytes in the resting condition.ConclusionsUsing isolated rat ventricular myocytes and the whole cell patch calmp technique, we found that visfatin could enhance the inward INa/Ca and decrease ICa,L in isolated rat ventricular myocytes, but it had no effect on I_KATP. These results suggest that the cardioprotective effect of visfatin may be partly attributed to its effect of enhancing the inward INa/Ca and the effect of decreasing ICa,L in cardiomyocytes, thus preventing calcium overload from occurring and alleviating I/R injury.