M. Martire et al., K+-evoked [H-3]D-aspartate release in rat spinal cord synaptosomes: Modulation by neuropeptide Y and calcium channel antagonists, J NEUROSC R, 62(5), 2000, pp. 722-729
This study was conducted to investigate mechanisms regulating the release o
f [H-3]D-aspattate (or endogenous glutamate) in the rat spinal cord. Presyn
aptic modulation of glutamate release was studied in superfused synaptosome
s depolarized with 20 mM KCl. Calcium-channel antagonists, omega -conotoxin
GVIA (omega -CgTx GVIA; N-type), nifedipine (L-type), and omega -conotoxin
MVIIC (omega -CmTx MVIIC; P/Q type), were used to characterize the voltage
-operated Ca2+ channels (VOCCs) involved in this release. Nifedipine had no
significant effect on the K+-evoked release of [H-3]D-aspartate, but the o
mega -conotoxins GVIA and MVIIC produced dose-dependent inhibitory effects
that were additive. The most substantial reduction (54.30% +/- 4.40%) was s
een with omega -CgTx GVIA, indicating that N-type channels play a major rol
e in the release of glutamate in this tissue. We investigated the effects o
f neuropeptide Y (NPY), NPY13-36, and [Leu(31)][Pro(34)]Npy on Ca2+-depende
nt, K+-evoked [H-3]D-aspartate release. NPY and NPY13-36 equipotently inhib
ited the release of glutamate in a concentration-dependent manner. The half
-maximal response was observed at about 12 nM; maximal inhibition of 44.22%
+/- 4.60% was achieved with 0.3 muM. The selective GABA(B) agonist (-)bacl
ofen inhibited K+-evoked [H-3]D-aspartate release from superfused spinal co
rd synaptosomes by 50.00% +/- 4.80% at 10 muM. When NPY13-36 and (-)baclofe
n were used together at maximal doses, their release-inhibiting effects wer
e not additive. In addition, neither of the agonists was able to enhance th
e inhibition produced by pretreating the synaptosomes with the selective in
hibitor of N-type VOCCs omega -CgTx GVIA. These results are consistent with
the hypothesis that presynaptic Y-2-like and GABA(B) receptors regulate gl
utamate release by blocking Ca2+ currents through N-type VOCCs. Characteriz
ation of the receptors that can inhibit the release of glutamate may provid
e useful information for treatment of conditions characterized by excessive
glutamatergic transmission in the spinal cord. J. Neurosci. Res. 62:722-72
9,2000. (C) 2000 Wiley-Liss, Inc.