Angiotensin II type 2 receptor stimulation of neuronal delayed-rectifier potassium current involves phospholipase A2 and arachidonic acid

Abstract

Angiotensin II (Ang II) elicits an Ang II type 2 (AT2) receptor- mediated increase in delayed-rectifier K+ current (I(K)) in neurons cultured from newborn rat hypothalamus and brainstem. This effect involves a pertussis toxin (PTX)-sensitive G1 protein and is abolished by inhibition of serine and threonine phosphatase 2A (PP-2A). Here, we determined that Ang II stimulates [3H]arachidonic acid (AA) release from cultured neurons via AT2 receptors. This effect of Ang II was blocked by inhibition of phospholipase A2 (PLA2) and by PTX. Because AA and its metabolites are powerful modulators of neuronal K+ currents, we investigated the involvement of PLA2 and AA in the AT2 receptor-mediated stimulation of I(K) by Ang II. Single- cell reverse transcriptase (RT)-PCR analyses revealed the presence of PLA2 mRNA in neurons that responded to Ang II with an increase in I(K). The stimulation of neuronal I(K) by Ang II was attenuated by selective inhibitors of PLA2 and was mimicked by application of AA to neurons. Inhibition of lipoxygenase (LO) enzymes significantly reduced both Ang II- and AA- stimulated I(K), and the 12-LO metabolite of AA 12S-hydroxyeicosatetraenoic acid (12S-HETE) stimulated I(K). These data indicate the involvement of a PLA2, AA, and LO metabolite intracellular pathway in the AT2 receptor- mediated stimulation of neuronal I(K) by Ang II. Furthermore, the demonstration that inhibition of PP-2A abolished the stimulatory effects of Ang II, AA, and 12S-HETE on neuronal I(K) but did not alter Ang II-stimulated [3H]-AA release suggests that PP-2A is a distal event in this pathway.