Concomitant acceleration of the activation and inactivation kinetics of the human delayed rectifier K+ channel (Kv1.1) by Ca2+-independent phospholipase A2

Abstract

The electrophysiologic sequelae of arachidonic acid release mediated by the major phospholipase A2 (PLA2) in electrically active tissues (i.e. the 40-kDa Ca2+-independent PLA2) were assessed in Sf9 cells expressing the human recombinant delayed rectifier K+ channel Kv1.1. Intracellular administration of Ca2+-independent PLA2 increased the rate of activation of the macroscopic current (from Tact = 6.25 ± 0.76 ms to τact, PLA2 = 2.78 ± 0.78 ms at 40 mV) and resulted in channel inactivation (from no observed inactivation to τinact = 103 ± 6 ms at 40 mV), which were: 1) dependent on the enrichment of Sf9 cell phospholipids in esterified arachidonic acid; 2) ablated by pretreatment of the PLA2 by the mechanism-based inhibitor (E)-6-(bromomethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one; and 3) manifest prior to development of alterations in cellular permeability. The bidirectional effects of Ca2+-independent PLA2 were indistinguishable from the effects of exogenously applied arachidonic acid (AA), which specifically and reversibly increased the rates of channel activation (from τact = 5.73 ± 0.88 ms to τact,AA = 1.91 ± 0.39 ms at 40 mV) and inactivation (from no observed inactivation to τinact = 76.6 ± 1.4 ms at 40 mV). These electrophysiologic alterations resulted from the effects of arachidonic acid per se since Sf9 cells did not produce oxygenated eicosanoid metabolites, and neither exogenous administration nor in situ generation of other fatty acids resulted in these effects. Collectively, these results unambiguously demonstrate the role of arachidonic acid per se on Kv1.1 electrophysiologic function and suggest the importance of Ca2+-independent PLA2 as an enzymic modulator of ion channel function in electrically active tissues.