SINGLE-CHANNEL PROPERTIES OF RECOMBINANT GABA(A) RECEPTORS CONTAININGGAMMA-2 OR DELTA-SUBTYPE EXPRESSED WITH ALPHA-1 AND BETA-3 SUBTYPES IN MOUSE L929 CELLS

1. To determine their contributions to GABA(A) receptor (GABAR) channe l properties, rat gamma 2L and delta subunits were acutely co-expresse d with alpha 1 and beta 3 subtypes in mouse L929 fibroblasts to produc e alpha 1 beta 3, alpha 1 beta 3 delta or alpha 1 beta 3 gamma 2L GABA R isoforms. 2. With whole-cell recording, the alpha 1 beta 3 isoform h ad relatively high sensitivity to GABA (EC50 2.1 mu M) and low maximum current amplitude. The alpha 1 beta 1 delta isoform had similar sensi tivity to GABA (EC50 2.8 mu M) and low current amplitude. The alpha 1 gamma 3 gamma 2L isoform had lower sensitivity to GABA (EC50 11.6 mu M ) and higher maximum current amplitude. 3. The single channel conducta nce of alpha 1 beta 3 channels was low (13 pS) compared with that of a lpha 1 beta 3 delta and alpha 1 beta 3 gamma 2L channels (27 pS). 4. T he single channel kinetic properties of the channels also differed. Th e alpha 1 beta 3 gamma 2L channel exhibited three open states, while t he alpha 1 beta 3 and alpha 1 beta 3 delta channels exhibited only two open states with mean dwell times similar to those of the two shorter open states of the alpha 1 beta 3 gamma 2L channel. All three channel s exhibited at least five closed states. Bursts of alpha 1 beta 3 delt a channels consisted primarily of only one or two openings, while thos e of alpha 1 beta 3 channels contained multiple openings. alpha 1 beta 3 gamma 2L channels exhibited burst kinetics typical for native GABAR s with several long openings per burst. 5. These results show that the alpha 1 beta 3 heterodimer formed a GABA-sensitive channel with compl ex gating kinetics. Addition of a delta subunit to form the alpha 1 be ta 3 delta heterotrimer altered the single channel conductance and the kinetic properties of the closed components, but did not affect the G ABA sensitivity of the receptor nor the open state kinetics. In contra st, addition of a gamma subunit (gamma 2L subtype) to produce the alph a 1 beta 3 gamma 2L heterotrimer affected the GABA sensitivity, channe l conductance and kinetic properties of both open and closed states.