EXOGENOUS GABA PERSISTENTLY OPENS CL- CHANNELS IN CULTURED EMBRYONIC RAT THALAMIC NEURONS

We recorded whole-cell Cl- currents in cultured embryonic rat thalamic neurons by brief applications of GABA or the structural analogue musc imol. In 17 of 141 neurons (12%) the Cl- current persisted for a minut e or more after the pipette was removed from the bath. Cl- current nev er persisted after muscimol exposure even in those cells exhibiting pe rsistent GABA-activated currents (PGC). The half decay times (T-50) of PGCs were exponentially and asymptotically related to the duration of GABA exposure and could be interrupted or completely aborted by low-p ressure application of saline. PGCs were insensitive to membrane poten tial, to Tiagabine, a nipecotic acid analogue known to block GABA upta ke, and persisted in Ca-o(2+)-free medium. Fluctuation analysis reveal ed that PGCs exhibited inferred Cl- channel properties whose kinetic c omponents and estimated average elementary conductance showed no signi ficant difference from those estimated during GABA exposure. The relat ive contribution of low frequency components was consistently reduced and that of high frequency components modestly increased during PGC co mpared to those recorded during GABA exposure. Taken together, the res ults suggest the existence of a superficial compartment in these embry onic neurons that can momentarily accumulate and release exogenous GAB A.