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The Journal of Neuroscience, April 15, 2000, 20(8):2867-2874
Heteromeric Assembly of GABABR1 and
GABABR2 Receptor Subunits Inhibits Ca2+ Current
in Sympathetic Neurons
Alexander K.
Filippov1,
Andrés
Couve1, 2,
Menelas N.
Pangalos3,
Frank
S.
Walsh3,
David A.
Brown1, and
Stephen J.
Moss1, 2
1 Department of Pharmacology and 2 Medical
Research Council Laboratory of Molecular Cell Biology, University
College London, London WC1E 6BT, United Kingdom, and
3 Department of Neuroscience, Smith-Kline Beecham, Harlow,
Essex CM19 5AW, United Kingdom
Neuronal GABAB receptors regulate calcium and potassium
currents via G-protein-coupled mechanisms and play a critical role in
long-term inhibition of synaptic transmission in the CNS. Recent studies have demonstrated that assembly of GABAB receptor
GABABR1 and GABABR2 subunits into functional
heterodimers is required for coupling to potassium channels in
heterologous systems. However whether heterodimerization is required
for the coupling of GABAB receptors to effector systems in
neurons remains to be established. To address this issue, we have
studied the coupling of recombinant GABAB receptors to
endogenous Ca2+ channels in superior cervical
ganglion (SCG) neurons using nuclear microinjection to introduce
both sense and antisense expression constructs. Patch-clamp
recording from neurons injected with both GABABR1a/1b and
GABABR2 cDNAs or with GABABR2 alone produced
marked baclofen-mediated inhibition of Ca2+ channel
currents via a pertussis toxin-sensitive
mechanism. The actions of baclofen were blocked by CGP62349, a specific
GABAB antagonist, and were voltage dependent.
Interestingly, SCGs were found to express abundantly
GABABR1 but not GABABR2 at the protein level.
To determine whether heterodimerization of GABABR1 and GABABR2 subunits was required for Ca2+
inhibition, the GABABR2 expression construct was
microinjected with a GABABR1 antisense construct. This
resulted in a dramatic decrease in the levels of the endogenous
GABABR1 protein and a marked reduction in the inhibitory
effects of baclofen on Ca2+ currents. Therefore our
results suggest that in neurons heteromeric assemblies of
GABABR1 and GABABR2 are essential to mediate
GABAergic inhibition of Ca2+ channel currents.
Key words:
GABABR1; GABABR2; Ca2+ channel; sympathetic neuron; antisense; G-protein
Copyright © 2000 Society for Neuroscience 0270-6474/00/2082867-08$05.00/0
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