Qy. Liu et al., UP-REGULATION OF GABA(A) CURRENT BY ASTROCYTES IN CULTURED EMBRYONIC RAT HIPPOCAMPAL-NEURONS, The Journal of neuroscience, 16(9), 1996, pp. 2912-2923
Embryonic rat hippocampal neurons were cultured on poly-D-lysine (PDL)
or a monolayer of postnatal cortical astrocytes to reveal putative ch
anges in neuronal physiology that involve astrocyte-derived signals du
ring the first 4 d of culture. GABA-induced Cl- current (I-GABA) was q
uantified using outside-out and whole-cell patch-clamp recordings begi
nning at 30 min, when cells had become adherent. The amplitude and den
sity (current normalized to membrane capacitance) of I-GABA in neurons
grown on astrocytes became statistically greater than that recorded i
n neurons grown on PDL after 2 hr in culture (HIC). Although the curre
nt density remained unchanged in neurons on astrocytes, that in neuron
s on PDL decreased and became statistically lower beginning after 2 HI
C. The differences in amplitude and density of I-GABA in the two group
s of neurons were maintained during the 4 d experiment. The upregulati
on effect of astrocytes on neuronal I-GABA required intimate contact b
etween the neuronal cell body and underlying astrocytes. Suppression o
f spontaneous Ca-c(2+) elevations in astrocytes by bis(2-aminophenoxy)
ethane-N,N,N',N'-tetra-acetic acid that was loaded intracellularly dec
reased their modulatory effects on I-GABA. I-GABA in all cells was blo
cked completely by bicuculline and exhibited virtually identical affin
ity constants, Hill coefficients, and potentiation by diazepam in the
two groups. Outside-out patch recordings revealed identical unitary pr
operties of I-GABA in the two groups. More channels per unit of membra
ne area could explain the astrocyte enhancement of I-GABA. The results
reveal that cortical astrocytes potentiate I-GABA in hippocampal neur
ons in a contact-dependent manner via a mechanism involving astrocyte
Ca-c(2+) elevation.