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KMID : 0617319970060010173
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Journal of Pharmacetical Sceiences Ewha Womans University
1997 Volume.6 No. 1 p.173 ~ p.178
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Subunit Composition Determines Picrotoxin and Bicuculline Sensitivity of Drosophila γ-Aminobutyric Acid Receptors
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ZHANG, HAI-GUANG
LEE, HWA-JUNG/ROCHELEAU, THOMAS/FFRENCH-CONSTANT, RICHARD H./JACKSON, MEYER B.
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Abstract
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Few γ-aminobutyric acid (GABA) receptor subunits have been cioned from insects. These include Resistance to dieldrin, or Rdl, and a homologue of the vertebrate GABA_A receptor βsubunit. Unlike most vertebrate GABA_A receptor subunits, Rdl forms a highly functional homomultimeric receptor. This receptor is picrotoxin (PTX) sensitive but bicuculline (BIC) insensitive and cannot be readily classified within the known GABA_A receptor subtypes. In contrast, functional expression of the βsubunit homologue has not been reported. We report that coinfection of cells with recombinant baculoviruses containing Rdl plus βsubunits induces GABA receptors with distinct pharmacological and kinetic properties. Coinfection produces two separate receptor populations: one highly sensitive to PTX but BIC insensitive (Rdl homomultimers) and the other PTX insensitive and BIC sensitive (Rdl plus β heteromultimers). Putative Rdl plus βchannels also show reduced GABA sensitivity; slow desensitization. rapid bursting, and shorter mean open time. These studies not only localize PTX and BIC sensitivity to two distinct GABA receptor subunits but also demonstrate assembly of two highly divergent GABA receptor subunits. Furthermore, the difference in channel conductance and gating between in vivo and recombinant channels implies the existence of uncharacterized GABA receptor subunits in Drosophlia.
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