Abstract
Activation of the platelet-activating factor (PAF) receptor leads to a decrease in outward current in murine ventricular myocytes by inhibiting the TASK-1 channel. TASK-1 carries a background or "leak" current and is a member of the two-pore domain potassium channel family. Its inhibition is sufficient to delay repolarization, causing prolongation of the action potential duration, and in some cases, early after depolarizations. We set out to determine the cellular mechanisms that control regulation of TASK-1 by PAF. Inhibition of TASK-1 via activation of the PAF receptor is protein kinase C (PKC)-dependent. Using isoform-specific PKC inhibitor or activator peptides in patch clamp experiments, we now demonstrate that activation of PKCepsilon is both necessary and sufficient to regulate murine TASK-1 current in a heterologous expression system and to induce repolarization abnormalities in isolated myocytes. Furthermore, site-directed mutagenesis studies have identified threonine 381, in the C-terminal tail of murine TASK-1, as a critical residue in this regulation.
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