title: Gabapentin activates ROMK1 channels by a protein kinase A (PKA)-dependent mechanism.
abstract: OBJECTIVE
  Gabapentin is an effective anticonvulsant. The major physiological function of renal outer medullary potassium (ROMK1) channels is to maintain the resting membrane potential (RMP). We investigated the effect of gabapentin on ROMK1 channels and the mechanism involved.
  
  
  METHODS
  Xenopus oocytes were injected with mRNA coding for wild-type or mutant ROMK1 channels and giant inside-out patch-clamp recordings were performed.
  
  
  RESULTS
  Gabapentin increased the activity of ROMK1 channels, concentration-dependently and enhanced the activity of wild-type and an intracellular pH (pH(i))-gating residue mutant (K80M) channels over a range of pH(i). Gabapentin also increased activity of channels mutated at phosphatidylinositol 4,5-bisphosphate (PIP(2))-binding sites (R188Q, R217A and K218A). However, gabapentin failed to enhance channel activity in the presence of protein kinase A (PKA) inhibitors and did not activate phosphorylation site mutants (S44A, S219A or S313A), mutants that mimicked the negative charge carried by a phosphate group bound to a serine (S44D, S219D or S313D), or a mutated channel with a positive charge (S219R). These findings show that gabapentin activates ROMK1 channels independently of the pH(i) and not via a PIP(2)-dependent pathway. The effects of gabapentin on ROMK1 channels may be due to a PKA-mediated phosphorylation-induced conformational change, but not to charge-charge interactions.
  
  
  CONCLUSIONS
  ROMK1 channels are the main channels responsible for maintaining the RMP during cellular excitation. Gabapentin increased the activity of ROMK1 channels by a PKA-dependent mechanism, reducing neuronal excitability, and this may play an important role in its antiepileptic effect.
authors.affiliation: Department of Pharmacology, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors.forename: C-H
authors.initials: CH
authors.lastname: Lee
authors.forename: T-S
authors.initials: TS
authors.lastname: Tsai
authors.forename: H-H
authors.initials: HH
authors.lastname: Liou
mesh_terms: D000588:Amines / Q000494:pharmacology*; D000818:Animals; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D003509:Cyclohexanecarboxylic Acids / Q000494:pharmacology*; D003627:Data Interpretation, Statistical; D005260:Female; D000077206:Gabapentin; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying / Q000819:agonists*; D011487:Protein Conformation; D014982:Xenopus laevis; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
chemical_list: D000588:Amines; D003509:Cyclohexanecarboxylic Acids; C086989:KCNJ1 protein, human; D019269:Phosphatidylinositol 4,5-Diphosphate; D024661:Potassium Channels, Inwardly Rectifying; D005680:gamma-Aminobutyric Acid; D000077206:Gabapentin; D017868:Cyclic AMP-Dependent Protein Kinases