Tumor necrosis factor α and ceramide depolarise the resting membrane potential of thyroid FRTL-5 cells via a protein kinase Cζ-dependent regulation of K+ channels

Abstract Tumor necrosis factor alpha (TNFα) alters the electrophysiological properties of many cell types. In thyroid cells however, the effects have not yet been elucidated. Here, we report the effect of TNFα and its second messenger ceramide on the resting membrane potential (RMP) of thyroid FRTL-5 cells. In patch-clamp experiments, we showed that TNFα and ceramide depolarise the RMP by inhibiting an acid-sensitive inwardly rectifying potassium current. This depolarisation depended on the activation of protein kinase Cζ (PKCζ), because it can be blocked by calphostin C, a PKC-inhibitory peptide and a specific inhibitor peptide for PKCζ. The activation of PKCζ was confirmed by Western blotting, in which a stimulation with TNFα led to the translocation of PKCζ to the particulate fraction. We conclude that TNFα and ceramide depolarise the RMP of thyroid FRTL-5 cells by attenuating a Ba 2+ - and acid-sensitive potassium conductance via activation of PKCζ.