Pharmacology
Pharmacodynamics
Gabapentin is a ligand of the α2δ calcium channel subunit. α2δ is an auxiliary protein connected to the main α1 subunit (the channel-forming protein) of high voltage activated voltage-dependent calcium channels (L-type, N-type, P/Q type, and R-type). Gabapentin is not a direct channel blocker: it exerts its actions by disrupting the regulatory function of α2δ and its interactions with other proteins. Gabapentin prevents delivery of the calcium channels to the cell membrane, reduces the activation of the channels by the α2δ subunit, decreases signaling leading to neurotransmitters release, and disrupts interactions of α2δ with NMDA receptors, neurexins, and thrombospondins. Out of the four known isoforms of α2δ protein, gabapentin binds with similar high affinity to two: α2δ-1 and α2δ-2. Most of the pharmacological properties of gabapentin are explained by its binding to just one isoform – α2δ-1.The endogenous α-amino acids L-leucine and L-isoleucine, which resemble gabapentin in chemical structure, bind α2δ with similar affinity to gabapentin and are present in human cerebrospinal fluid at micromolar concentrations. They may be the endogenous ligands of the α2δ subunit, and they competitively antagonize the effects of gabapentin. Accordingly, while gabapentin has nanomolar affinity for the α2δ subunit, its potency in vivo is in the low micromolar range, and competition for binding by endogenous L-amino acids is likely to be responsible for this discrepancy.Gabapentin is a potent activator of voltage-gated potassium channels KCNQ3 and KCNQ5, even at low nanomolar concentrations.
Hepatic porphyrias is a form of porphyria in which toxic porphyrin molecules build up in the liver. Hepatic porphyrias can result from a number of different enzyme deficiencies.Examples include (in order of synthesis pathway):
Acute intermittent porphyria
Porphyria cutanea tarda and Hepatoerythropoietic porphyria
Hereditary coproporphyria
Variegate porphyria

See also
Erythropoietic porphyria
Givosiran

References
External links

Porphyrias,+Hepatic at the US National Library of Medicine Medical Subject Headings (MeSH)
www.drugs-porphyria.com
www.porphyria-europe.com