Oxidative modulation of the transient potassium current IA by intracellular arachidonic acid in rat CA1 pyramidal neurons

Oxidative stress affects cellular membrane lipids and proteins. Using whole-cell patch-clamp recording we demonstrate differential oxidative inhibition of voltage-gated transient (I-A) and delayed rectifier [I-K(V)] K+ currents by arachidonic acid (AA) and H2O2 in CA1 neurons in hippocampal slice. We show that intracellular application of 1 pM AA or its non-metabolizable analog eicosatetraynoic acid (100 pM) reduced I-A by similar to 42% but did not affect I-K(V). AA shifted the voltage dependence of steady-state inactivation of I-A by 12 mV to more negative potentials whereas the rate of inactivation was unchanged. Surprisingly, intracellular glutathione (GSH, 20 mM) enhanced the effect of AA on maximal I-A (-62%) and with AA slowed inactivation of I-A. The combination of GSH and extracellular ascorbate (0.4 mM) prevented reduction of I-A by AA. Intracellular Trolox (a vitamin E analog, 10 mu M) reduced I-A by 61%and I-K(V) by 39%. Like AA, intracellular Trolox caused a 10-mV left shift of I-A steady-state inactivation but Trolox and AA did not cause a shift when coapplied. Extracellular Trolox (100 mu M) had no effects on I-A. H2O2 (80 mu M) reduced both I-A and I-K(V) in a GSH- and ascorbate-sensitive manner and slowed the rate of inactivation of I-A by a factor of 2. Coapplication of H2O2 with GSH and extracellular ascorbate caused similar to 22 mV negative shifts of both steady-state inactivation and activation. We conclude that AA is extremely potent in affecting I-A by oxidative modifications. Antioxidants can augment these effects, probably by catalysis of the underlying reactions between oxidants and I-A channel proteins.