Tumor necrosis factor-alpha (TNF-alpha) affects contractility and ionic currents in the heart. However, the electrophysiological effects, especially on delayed rectifier K currents (IK), have not yet been fully elucidated. We examined the effects of TNF-alpha on IK. Using a voltage-clamp method, IK was measured in guinea pig ventricular myocytes in the basal state and after pharmacological intervention. To specify the site of the action of TNF-alpha, the myocytes were incubated with pertLISSiS toxin or Al-olcoylethanolarnine, it cerarnidase inhibitor, and IK was measured. TNF-alpha suppressed IK when it was enhanced by isoproterenol, histamine or forskolin but not in the basal state or when IK was augmented by an internal application of cyclic AMP. Both pre-itICUbation with pertUSSiS toxin and N-olcoylethanolamine abolished the inhibitory action of TNF-alpha on isoproterenol-augmented IK. TNF-alpha inhibits IK, mainly IKs, when it is augmented by PKA as a result of the generation of sphingosine. (c) 2006 Elsevier Inc. All rights reserved.