Table 1

Methods for recognition of γ-aminobutyric acidA receptor subtypes in situ

1.  High-resolution labeling methodsSpatial separation of receptor
 a.  Immunofluorescence subtypes must be adequate
 b.  Immunocytochemical reaction
 c.  Freeze-fracture/antibody labeling
 d.  Antibody labeling in postembedding electromicroscopy1-a
2.  Single cell RT-PCR,1-bcombined with patch-clamp recordinga.  Only one subtype is present
b.  Large cells are required
c.  All the receptor mRNAs present must give rise to the assembled receptor1-c
3.  Use of an absolutely subtype-specific drug (e.g., furosemide, for α6β2/3 γ2)1-d a.  Specific for one defined composition; cases will be rare
b.  Patch-clamping must be applicable, or the drug must be labeled, for in situ binding
  • 1-a For example, using sized gold particles (Nusseret al., 1996).

  • 1-b RT-PCR, reverse transcriptase-polymerase chain reaction.

  • 1-c Examples to the contrary are given by Williamson and Pritchett (1994).

  • 1-d This specificity for this drug has been reported by Korpiet al. (1995), but application at the microscopic level of this or any other subtype-specific ligand has not been reported yet. Furosemide as a noncompetitive antagonist selects α4β3 γ2 receptors as well as α6β2/3 γ2 receptors, but is 14-fold less active at the former (Wafford et al., 1996).