Brain astrocyte‐derived EETs and 20‐EHTE elicit opposing actions on calcium movement and KCa channel current activities in astrocytes

Abstract

Cultured brain astrocytes incubated with arachidonic acid (AA) produce four CYP epoxygenase metabolites epoxyeicosatrienoic acids (EETs) 5,6‐, 8,9‐, 1,12‐and 14,15‐EET. The formation and action of 20‐hydroxyeicosatrienoic acid (20‐HETE) in brain astrocytes is not known. We investigated the capacity of brain astrocytes to express CYP‐4A‐ù‐hydroxylase protein and to convert AA to 20‐HETE. We also investigated the effects of 20‐HETE on membrane potential, KCa single‐channel activity, and on intracellular Ca2+ ([Ca2+]i) levels in cultured astrocytes. We found that astrocytes express CYP‐4A‐ù‐hydroxylase at the transcript and protein levels and produce 20‐HETE when incubated with AA. Treatment of astrocytes with 20‐HETE (100 nM) inhibited the openings of KCa single‐channel currents in cell‐attached patches and caused astrocyte membrane potential depolarization, whereas it had no effect on [Ca2+]i levels in astrocytes loaded with the Ca2+ probe Fura‐2AM. In contrast, treatment of cultured astrocytes with one of the EETs, 11.12‐EET increased [Ca2+]i level and activated astrocyte KCa channel currents. These findings indicate that the EETs and 20‐HETE produced and released by astrocytes could have opposing physiological actions at astrocyte end feet, which might be crucial for the maintenance of constant hyperemic cerebral blood flow during increased neuronal activation.