PKA-mediated phosphorylation is a novel mechanism for levetiracetam, an antiepileptic drug, activating ROMK1 channels

Abstract

Levetiracetam (LEV) is an effective antiepileptic drug (AED) with distinct mechanism from the conventional AEDs. The major physiological function of ROMK1 channels is to maintain the resting membrane potential (RMP). In this study, we investigated the mechanisms underling LEV on ROMK1 channels. Xenopus oocytes were injected with mRNA to express the wild-type or mutant ROMK1 channels. Giant inside-out patch clamp recordings were performed to study the effect of LEV on these channels. LEV increased the activity of ROMK1 channels in a concentration-dependent manner and enhanced both wild-type and pH i gating residue mutant (K80M) channels over a range of pH i values. LEV activated the mutated channels at PIP 2-binding sites (R188Q, R217A and K218A) and PKC-phosphorylation sites channels (S4A, S183A, T191A, T193A, S201A and T234A). However, this drug failed to enhance the channel activity in the presence of PKA inhibitors and did not activate the mutants of PKA-phosphorylation sites on C-terminal (S219A, S313A) and the constructed mutants (S219D and S313D) that mimic the negative charge carried by a phosphate group bound to a serine. Our results demonstrated PKA-mediated phosphorylation is a novel mechanism for LEV activating ROMK1 channels. These findings show that LEV activates ROMK1 channels independently from pH i and not via a PIP 2- or PKC-dependent pathway. The effects of LEV may come from the PKA-induced conformational change but not charge–charge interaction in ROMK1 channels. Enhancing the activity of ROMK1 channels may be an important molecular mechanism for the antiepileptic effects of LEV in restoring neuronal RMP to prevent seizure spreading.