The nomenclature of individual families of ligand-gated ion channels (LGICs) has developed independently since these receptors were first identified, resulting in a variety of nomenclature systems. As we no longer expect to discover large numbers of LGIC receptor subunits in the human genome, but are continuing to find heteromeric receptor combinations, NC-IUPHAR has re-examined the naming of LGIC subunits (1) and the evidence needed to accept a receptor multimer as functional in vivo (2,3). The nomenclature recommendations of NC-IUPHAR are summarised below.
- Glutamate receptor subunit names should be standardised (see table) using a logical and consistent scheme that harmonises with their HUGO gene names (1).
- Those ionotropic GABA receptors that have unofficially been denoted GABAC are now recognised as a subset of the GABAA receptors, and NC-IUPHAR recommends that the GABAC appellation should no longer be used (2,3).
- The use of subscripts within subunit names should be avoided (1).
- In naming receptor multimers, subunits should be indicated in alphabetical or numerical order (neither subscripted or superscripted) and where stoichiometry is to be indicated the subunit should be placed in parentheses followed by the number of units indicated by a subscripted numeral (1).
LGICs are multimeric proteins, often with constituent subunits that are encoded by more than one gene. This raises complex issues of nomenclature and difficulties in defining the receptor types that are actually functionally expressed in native systems. These issues are addressed in two papers by Olsen and Sieghart (2,3), using the complex GABAA receptor family as an exemplar. They have developed criteria that class subunit assemblies as (i) identified receptors; (ii) receptors existing with high probability and (iii) receptors that are tentative upon currently available evidence.
- (1) Collingridge, GL et al. (2009). A nomenclature for ligand-gated ion channels. Neuropharmacology. 56: 2-5 [PDF][Full Text]
- (2) Olsen, RW, Sieghart, W. (2008). International Union of Pharmacology. LXX. Subtypes of γ-aminobutyric acidA receptors: classification on the basis of subunit composition, pharmacology, and function. Update. Pharmacol Rev. 60: 243-60. [PDF][Full Text]
- (3) Olsen, RW, Sieghart, W. (2009). GABAA receptors: Subtypes provide diversity of function and pharmacology. Neuropharmacology. 56: 141-148 [PDF][Full Text]