Go transduces GABAB-receptor modulation of N-type calcium channels in cultured dorsal root ganglion neurons

Abstract

High-voltage-activated (HVA) calcium channel currents (IBa) were recorded from acutely replated cultured dorsal root ganglion (DRG) neurons. IBa was irreversibly inhibited by 56.9 +/- 2.7% by 1 microM omega-conotoxin-GVIA (omega-CTx-GVIA), whereas the 1,4-dihydropyridine antagonist nicardipine was ineffective. The selective gamma-aminobutyric acidB (GABAB) agonist, (-)-baclofen (50 microM), inhibited the HVA IBa by 30.7 +/- 5.4%. Prior application of omega-CTx-GVIA completely occluded inhibition of the HVA IBa by (-)-baclofen, indicating that in this preparation (-)-baclofen inhibits N-type current. To investigate which G protein subtype was involved, cells were replated in the presence of anti-G protein antisera. Under these conditions the antibodies were shown to enter the cells through transient pores created during the replating procedure. Replating DRGs in the presence of anti-G(o) antiserum, raised against the C-terminal decapeptide of the G alpha o subunit, reduced (-)-baclofen inhibition of the HVA IBa, whereas replating DRGs in the presence of the anti-Gi antiserum did not. Using anti-G alpha o antisera (1:2000) and confocal laser microscopy, G alpha o localisation was investigated in both unreplated and replated neurons. G alpha o immunoreactivity was observed at the plasma membrane, neurites, attachment plaques and perinuclear region, and was particularly pronounced at points of cell-to-cell contact. The plasma membrane G alpha o immunoreactivity was completely blocked by preincubation with the immunising G alpha o undecapeptide (1 microgram.ml-1) for 1 h at 37 degrees C. A similar treatment also blocked recognition of G alpha o in brain membranes on immunoblots.(ABSTRACT TRUNCATED AT 250 WORDS)

Exogenous nerve growth factor attenuates opioid-induced inhibition of voltage-activated Ba2+ currents in rat sensory neurons

“…The βγ subunits of the G protein heterotrimer dissociate from the α subunit and mediate inhibition of VGCC by direct binding to the α subunit of the VGCC (Herlitze et al, 1996;Ikeda, 1996;Zamponi et al, 1997;Delmas et al, 1998;Zamponi and Snutch, 1998). Because the GABA B receptor has also been shown to inhibit VGCC by activating G o (Menon-Johansson et al, 1993;Kajikawa et al, 2001), the lack of effect of NGF on baclofen-mediated inhibition of I Ba in the present study indicates that NGF did not alter the function of G protein subunits or their coupling to VGCC. Further evidence for normal function downstream of the opioid receptor is the lack of effect of NGF on direct G protein activation with GTP-γ-S.…”

Decay in Prepulse Facilitation of Calcium Channel Currents by Gi/o-Protein Attenuation in Hamster Submandibular Ganglion Neurons, But Not Gq/11.

“…GPCR activated by neurotransmitters couple to the carboxy-terminals of G-protein ␣ subunits, and polyclonal antibodies raised against C-terminal peptide sequences of different G␣ subunits have been shown to functionally antagonize neurotransmitter modulation of VDCCs (e.g. anti-G i/o 31,32) ; anti-G q/11 37) ). The results in this paper thus provide a possible mechanism for effects of G i/o -, but not G q/11 -protein, in the inhibitory regulation of VDCCs and dissociation of ␤␥ subunits from heterotrimeric G-protein to serve in signal transduction.…”

Molecular Structure and Physiological Functions of GABABReceptors

“…Evidence for a coupling of GABA B receptors to G proteins came from the sensitivity of agonist affinity to GTP analogs (10,144). Studies using N-ethylmaleimide (NEM), islet activated protein (IAP), pertussis toxin, or antisense knock-down provided evidence that GABA B receptors predominantly couple to G i ␣-and G o ␣-type G proteins (9,59,122,223,228). It is now well established that presynaptic GABA B receptors repress Ca 2ϩ influx by inhibiting Ca 2ϩ channels in a membrane-delimited manner via the G␤␥ subunits (see sect.…”