Rapid negative inotropic effect induced by TNF-α in rat heart perfused related to PKC activation

Myocardial depression, frequently observed in septic shock, is mediated by circulating molecules such as cytokines. TNF-alpha appears to be the most important pro-inflammatory cytokine released during the early phase of a septic shock. It was previously shown that TNF-alpha had a negative inotropic effect on myocardium. Now, the aim of this study was to investigate the effects of the activation of PKC by TNF-alpha on heart function, and to determine if this cytokine could induce a decrease of membrane excitability. Isolated rat hearts (n = 6) were perfused with Tyrode solution containing TNF-alpha at 20 ng/ml during 30 min by using a Langendorff technique. Expressions of PKC-alpha and PKC-epsilon were analysed by western blot on membrane and cytosol proteins extracted from ventricular myocardium. Patch clamp was performed on freshly isolated cardiomyocytes (n = 8). Compared to control situation, 30 min of TNF-alpha perfusion led to cardiac dysfunction with a decrease of the heart rate (-83%), the force (-20%) and speed of relaxation (-18%) and the coronary flow (-25%). This is associated with an activation and a membrane targeting of both PKC-alpha and PKC-epsilon isoforms in ventricle with respectively +123% and +54% compared to control hearts. Nevertheless, TNF-alpha had no significant effect on voltage-gated sodium current (109.0% +/- 12.5) after addition of the cytokine when compared to control. These results showed that TNF-alpha had a negative inotropic effect on the isolated rat heart and can induce PKC activation leading to an impaired contractility of the heart. However the early heart dysfunction induced by the cytokine was not associated to a decrease of cardiomyocytes membrane excitability as it has been evidenced in skeletal muscle fibres.