| The balance between excitation and inhibition is essential for the normal function of the CNS. Glycine receptors(GlyRs) binding to its agonist trigger the opening of the cloride-selective channel spanning the plasma membrane. Glycinergic synapses mediate fast inhibitory neurotransmission in the adult mammalian CNS. Considerable studies have implicated GlyR gene in the pathology of neurological disorders. Patients suffering from diseases caused by diminished inhibition would probably benefit most from facilitated glycinergic inhibition. Hence, GlyRs constitute promising targets for designing novel therapeutic strategies for the treatment of the diseases.Here we show that capsazepine(CPZ), a competitive TRPV1 antagonist, inhibits glycine-evoked current in CNS neurons. However, TRPV1 antagonist curcumin does not supress GlyR-mediated current. In addition, CPZ decreased glycine-induced response in TRPV1 knock-out mice. These evidences suggest that CPZ inhibition on GlyRs is independent of TRPV1. Furthermore, CPZ inhibits different GlyR isoforms. CPZ effectively reduces the maximal current mediated by native glycine receptors without altering the EC50 and the Hill coefficient, indicating a non-competitive action of CPZ. Immunocytochemical data show that CPZ does not significantly change the surface number or intensity of GlyRs, suggesting that CPZ reduces GlyR-mediated current not by regulating its trafficking and the effect is further confirmed by the spinal cord neuron surface biotinylation experiment.Single channel recordings in cell-attached configuration show that CPZ reduces the open probability of GlyRs without changing the channel conductance, but the inhibitory effect is not detectable in outside-out patch clamp recordings, indicating that CPZ does not directly bind to GlyRs. Taken together, CPZ reduces glycine-evoked current independent of TRPV1, and our results may indicate that there is an intracellular signaling involved in the CPZ inhibitory effects on GlyRs in CNS. |
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