Regulation of K(Ca)2.3 and endothelium-dependent hyperpolarization (EDH) in the rat middle cerebral artery: the role of lipoxygenase metabolites and isoprostanes

Background and Purpose. In rat middle cerebral arteries, endothelium-dependent hyperpolarization (EDH) is mediated by activation of calcium-activated potassium (K(Ca)) channels specifically K(Ca)2.3 and K(Ca)3.1. Lipoxygenase (LOX) products function as endothelium-derived hyperpolarizing factors (EDHFs) in rabbit arteries by stimulating K(Ca)2.3. We investigated if LOX products contribute to EDH in rat cerebral arteries. Methods. Arachidonic acid (AA) metabolites produced in middle cerebral arteries were measured using HPLC and LC/MS. Vascular tension and membrane potential responses to SLIGRL were simultaneously recorded using wire myography and intracellular microelectrodes. Results. SLIGRL, an agonist at PAR2 receptors, caused EDH that was inhibited by a combination of K(Ca)2.3 and K(Ca)3.1 blockade. Non-selective LOX-inhibition reduced EDH, whereas inhibition of 12-LOX had no effect. Soluble epoxide hydrolase (sEH) inhibition enhanced the K(Ca)2.3 component of EDH. Following NO synthase (NOS) inhibition, the K(Ca)2.3 component of EDH was absent. Using HPLC, middle cerebral arteries metabolized (14)C-AA to 15- and 12-LOX products under control conditions. With NOS inhibition, there was little change in LOX metabolites, but increased F-type isoprostanes. 8-iso-PGF(2α) inhibited the K(Ca)2.3 component of EDH. Conclusions. LOX metabolites mediate EDH in rat middle cerebral arteries. Inhibition of sEH increases the K(Ca)2.3 component of EDH. Following NOS inhibition, loss of K(Ca)2.3 function is independent of changes in LOX production or sEH inhibition but due to increased isoprostane production and subsequent stimulation of TP receptors. These findings have important implications in diseases associated with loss of NO signaling such as stroke; where inhibition of sEH and/or isoprostane formation may of benefit.