M. Martina et al., WHOLE-CELL AND SINGLE-CHANNEL PROPERTIES OF A NEW GABA RECEPTOR TRANSIENTLY EXPRESSED IN THE HIPPOCAMPUS, Journal of neurophysiology, 73(2), 1995, pp. 902-906
1. The patch-clamp technique was used to characterize, in acutely diss
ociated CA3 rat hippocampal neurons, the whole cell and single channel
properties of a novel response to gamma-aminobutyric acid (GABA) pres
ent only during a restricted period of post natal development. 2. At p
ostnatal days 0-10 (P0-P10) both GABA (100 mu M) and isoguvacine (50 m
u M) evoked at a holding potential of -50 mV, in symmetrical chloride
solution, whole cell inward currents. Bicuculline blocked the response
to isoguvacine but only reduced the response to GABA (from 512 +/- 13
7 pA to 60 +/- 13 pA, mean +/- SE). After P12, bicuculline abolished t
he response to GABA. 3. The bicuculline insensitive GABA currents were
Cl- mediated and antagonized by picrotoxin. The desensitization rate
was slower than the conventional bicuculline-sensitive response. The p
eak to plateau ratio induced by 0.1 or 1 mM of GABA shifted from 4.6 /- 0.4 and 17.7 +/- 2.6 to 1.5 +/- 0.1 and 3.1 +/- 0.5 in the absence
or in the presence of bicuculline, respectively. The recovery from des
ensitization was significantly faster for the bicuculline insensitive
responses. 4. In excised outside-out patches, GABA (20 mu M) activated
, in the presence of bicuculline (100 mu M), single channel currents h
aving conductances of 14, 22. and 31 pS. These values were similar to
those obtained in the same preparation, in the absence of bicuculline.
5. These findings suggest that this new receptor type, which mediates
bicuculline-insensitive responses with slow kinetics, may potentiate
the depolarizing action of GABA during a critical period of postnatal
development and therefore play a crucial role in synaptogenesis.