Two different modes of action of pentobarbital at glycine receptor channels

Thiopental inhibits glycine receptor function in acutely dissociated rat spinal dorsal horn neurons

Whole-cell patch-clamp was used to assess the modulatory effect of thiopental (Thio) on glycine (Gly) receptor in mechanically dissociated rat spinal dorsal horn neurons. It was found that Thio inhibited the amplitude, accelerated the desensitization and prolonged the deactivation of Gly-induced currents (IGly) in a concentration-dependent manner. In addition, a rebound current occurred after washout of the co-application of Gly and Thio in most neurons tested. Moreover, the inhibitory effect of Thio was not the result of cross-inhibition between Gly and GABAA receptors. Furthermore, taurine-induced currents, a low-affinity agonist for Gly receptors, were also markedly inhibited by Thio in a similar way to IGly. These results indicate that Thio suppresses Gly receptor function and suggest that Thio anesthetic actions might not be mediated by Gly receptors. We speculate that the weak muscle relaxation and the limited analgesic effects observed during Thio anesthesia may attribute to its inhibitory effects on Gly receptors.

Cytoprotection by glycine against ATP-depletion-induced injury is mediated by glycine receptor in renal cells

It is known that glycine protects mammalian cells against ischaemic cell injury by preventing cellular membrane leakage. However, the molecular mechanisms have not yet been clearly elucidated. The purpose of the present study was to clarify whether GlyR (glycine receptor) acts as a key mediator in cytoprotection of glycine. cDNA encoding human GlyRa1 (a1-subunit of glycine receptor) was transfected into HEK-293 cells. The membrane integrity of the cells with or without GlyRa1 was examined by the uptake of marker compounds, the release of LDH (lactate dehydrogenase) and the exclusion of Trypan Blue. Glycine prevented the permeability of 70 kDa dextrans and 140 kDa LDH in the cells in which GlyR was expressed under conditions of ATP depletion. The inhibition of endogenous GlyR expression by RNA interference attenuated the cytoprotection by glycine. Furthermore, the mutation of Tyr202 to phenylalanine in GlyRa1 blocked the glycine-mediated cytoprotection, while the mutation of Tyr202 to leucine abolished the cytoprotection by strychnine. Our results suggested that the cytoprotection of glycine against ATP-depletion-induced injury might be mediated by GlyR.

Interaction of topiramate with glycine receptor channels

Glycine receptor channels are pentameric ligand-gated ion channels that respond to the application of inhibitory neurotransmitters by opening of a chloride-selective central pore. Topiramate (TPM) is a broad-spectrum antiepileptic drug used as add-on or monotherapy for focal seizures. In the present study the interaction of TPM with glycine receptor channels was studied on outside-out patches from HEK293 cells expressing alpha1beta glycine receptor channels. The patch clamp techniques combined with ultra fast solution exchange enabled us to investigate the kinetics of receptor channels in presence of TPM. Our study showed no agonistic or potentiating effect for TPM on glycine receptor channels. However, in presence of 1 mM glycine + 1 mM TPM, the desensitization got faster and the peak current amplitude decreased. After the end of glycine + TPM pulses, off-currents occurred, suggestive for a specific channel block mechanism.

Effects of propofol on recombinant AMPA receptor channels

The interaction of the anaesthetic propofol with recombinant human AMPA-type glutamate receptor channels was investigated by a patch-clamp study using fast agonist application techniques. Despite the marked effects of propofol on inhibitory synaptic transmission and voltage gated sodium channels, there is also evidence for a specific pharmacological action on AMPA receptors. In our study, we observed a deceleration of AMPA receptor channel desensitization in the prolonged presence of glutamate and propofol that is likely to account for the enhancement of ion currents through AMPA receptor channels observed in previous studies. While there was an increase in the rate and extent of desensitization at glutamate receptor 1, glutamate receptor 2, and glutamate receptor 3 AMPA receptors, no affection of current rise time, peak current amplitude, and deactivation properties was observed. Thus, our findings point to an isolated interaction with processes that control desensitization of AMPA receptor channels rather than indicating an interaction with channel opening and closing processes due to agonist binding and unbinding. The pharmacological effect described resembles in part that of compounds like cyclothiazide and aniracetam which are known to interact with channel desensitization.