Modulation by general anaesthetics of rat GABAA receptors comprised of a1b3 and b3 subunits expressed in human embryonic kidney 293 cells

1 Radioligand binding and patch-clamp techniques were used to study the actions of g-aminobutyric acid (GABA) and the general anaesthetics propofol (2,6-diisopropylphenol), pentobarbitone and 5a-pregnan3a-ol-20-one on rat a1 and b3 GABAA receptor subunits, expressed either alone or in combination. 2 Membranes from HEK293 cells after transfection with a1 cDNA did not bind signi®cant levels of [S]-tert-butyl bicyclophosphorothionate ([S]-TBPS) (50.03 pmol mg protein). GABA (100 mM) applied to whole-cells transfected with a1 cDNA and clamped at 760 mV, also failed to activate discernible currents. 3 The membranes of cells expressing b3 cDNAs bound [S]-TBPS (*1 pmol mg protein). However, the binding was not in ̄uenced by GABA (10 nM± 100 mM). Neither GABA (100 mM) nor picrotoxin (10 mM) a€ected currents recorded from cells expressing b3 cDNA, suggesting that b3 subunits do not form functional GABAA receptors or spontaneously active ion channels. 4 GABA (10 nM ± 100 mM) modulated [S]-TBPS binding to the membranes of cells transfected with both a1 and b3 cDNAs. GABA (0.1 mM±1 mM) also dose-dependently activated inward currents with an EC50 of 9 mM recorded from cells transfected with a1 and b3 cDNAs, clamped at 760 mV. 5 Propofol (10 nM± 100 mM), pentobarbitone (10 nM± 100 mM) and 5a-pregnan-3a-ol-20-one (1 nM± 30 mM) modulated [S]-TBPS binding to the membranes of cells expressing either a1b3 or b3 receptors. Propofol (100 mM), pentobarbitone (1 mM) and 5a-pregnan-3a-ol-20-one (10 mM) also activated currents recorded from cells expressing a1b3 receptors.