G protein {beta}{gamma} subunits mediate presynaptic inhibition of transmitter release from rat superior cervical ganglion neurones in culture.
The activation of presynaptic G protein-coupled receptors (GPCRs) is widely reported to inhibit transmitter release; however, the lack of accessibility of many presynaptic terminals has limited direct analysis of signalling mediators. We studied GPCR-mediated inhibition of fast cholinergic transmission between superior cervical ganglion neurones (SCGNs) in culture. The adrenoceptor agonist noradrenaline (NA) caused a dose-related reduction in evoked excitatory postsynaptic potentials (EPSPs). NA-induced EPSP decrease was accompanied by effects on the presynaptic action potential (AP), reducing AP duration and amplitude of the after-hyperpolarization (AHP), without affecting the pre- and postsynaptic membrane potential. All effects of NA were blocked by yohimbine and synaptic transmission was reduced by clonidine, consistent with an action at presynaptic alpha2-adrenoceptors. NA-induced inhibition of transmission was sensitive to pre-incubation of SCGNs with pertussis toxin (PTX), implicating the involvement of Galpha(i/o)betagamma subunits. Expression of Galpha transducin, an agent which sequesters G protein betagamma (Gbetagamma) subunits, in the presynaptic neurone caused a time-dependent attenuation of NA-induced inhibition. Injection of purified Gbetagamma subunits into the presynaptic neurone inhibited transmission, and also reduced the AHP amplitude. Furthermore, NA-induced inhibition was occluded by pre-injection of Gbetagamma subunits. The Ca(2+) channel blocker Cd(2+) mimicked NA effects on transmitter release. Cd(2+), NA and Gbetagamma subunits also inhibited somatic Ca(2+) current. In contrast to effects on AP-evoked transmitter release, NA had no clear action on AP-independent EPSPs induced by hypertonic solutions. These results demonstrate that Gbetagamma subunits functionally mediate inhibition of transmitter release by alpha2-adrenoceptors and represent important regulators of synaptic transmission at mammalian presynaptic terminals.
Stephens
Gary J
GJ
Department of Pharmacology, University College London, Gower Street, London WC1E 6BT, UK. g.stephens@ucl.ac.uk
Mochida
Sumiko
S
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D020013:Calcium Signaling / Q000502:physiology; D002478:Cells, Cultured; D044387:GTP-Binding Protein beta Subunits / Q000378:metabolism*; D044388:GTP-Binding Protein gamma Subunits / Q000378:metabolism*; D009433:Neural Inhibition / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D017729:Presynaptic Terminals / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D017783:Superior Cervical Ganglion / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*
D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D018341:Receptors, Adrenergic, alpha-2; D043562:Receptors, G-Protein-Coupled