The main purpose of this study was to determine the subchronic effects of low concentrations of tumor necrosis factor alpha (TNF alpha) on the inotropic response and on the cellular level of high energy phosphates of cardiomyocytes. Therefore, the inotropic response of cultured neonatal rat heart cells to 10(-5) M isoproterenol-, 10(-6) M ouabain-, 10(-5) M forskolin- and 2,4 mM calcium-perfusion was studied 24 h after exposure to TNF alpha (0.01/0.1/1/10/100 U/ml). In parallel experiments high energy phosphates (CP, ATP, ADP, AMP) were determined by high performance liquid chromatography. Furthermore, the reversibility of TNF alpha-induced changes was studied after washout of TNF alpha or after administration of anti-TNF alpha-antibody. Whereas control cells showed an increase of cell wall motion to 150 +/- 5% of baseline value during 10(-5) M isoproterenol-perfusion respectively 180 +/- 7% during 2,4 mM calcium-perfusion, 24 h exposure of the cells to 1 U/ml up to 100 U/ml TNF alpha resulted in an inhibition of the inotropic response. Almost complete inhibition was observed 12 h after exposure to TNF alpha and was reversible 12 h after administration of the anti-TNF alpha-antibody. If the cells were perfused with 10(-6) M ouabain or 10(-5) M forskolin, a similar inhibition of the inotropic response was observed 24 h after TNF alpha-exposure. Determination of high energy phosphates showed that 24 h TNF alpha-exposure resulted in a reversible decrease of ATP, ADP, AMP and CP by 30-40% (p < 0.05). However, a similar reduction of cellular high energy phosphate levels using a TNF alpha independent mechanism (2,5 mM 2-deoxy-D-glucose) did not inhibit the inotropic response of the cardiomyocytes. From our results we conclude that subchronic exposure to low concentrations of TNF alpha resulted in an almost complete but reversible inhibition of the response of cardiomyocytes to different inotropic agents suggesting that a common final step of the inotropic cascade might be altered by TNF alpha. Though energy metabolism of TNF alpha exposed cells was affected also, reduction of high energy phosphate levels alone did not explain the observed inhibition of the inotropic response of the cardiomyocytes.
