Determination of the extracellular concentration of glycine in the rat spinal cord dorsal horn by quantitative microdialysis

Effects of nitrous oxide on glycinergic transmission in rat spinal neurons

We investigated the effects of nitrous oxide (N₂O) on glycinergic inhibitory whole-cell and synaptic responses using a "synapse bouton preparation," dissociated mechanically from rat spinal sacral dorsal commissural nucleus (SDCN) neurons. This technique can evaluate pure single- or multi-synaptic responses from native functional nerve endings and enable us to accurately quantify how N₂O influences pre- and postsynaptic transmission. We found that 70 % N₂O enhanced exogenous glycine-induced whole-cell currents (I_Gly) at glycine concentrations lower than 3 × 10^-5 M, but did not affect I_Gly at glycine concentrations higher than 10^-4 M. N₂O did not affect the amplitude and 1/e decay-time of both spontaneous and miniature glycinergic inhibitory postsynaptic currents recorded in the absence and presence of tetrodotoxin (sIPSCs and mIPSCs, respectively). The decrease in frequency induced by N₂O was observed in sIPSCs but not in mIPSCs, which was recorded in the presence of both tetrodotoxin and Cd²⁺, which block voltage-gated Na⁺ and Ca²⁺ channels, respectively. N₂O also decreased the amplitude and increased the failure rate and paired-pulse ratio of action potential-evoked glycinergic inhibitory postsynaptic currents. N₂O slightly decreased the Ba²⁺ currents mediated by voltage-gated Ca²⁺ channels in SDCN neurons. We found that N₂O suppresses glycinergic responses at synaptic levels with presynaptic effect having much more predominant role. The difference between glycinergic whole-cell and synaptic responses suggests that extrasynaptic responses seriously modulate whole-cell currents. Our results strongly suggest that these responses may thus in part explain analgesic effects of N₂O via marked glutamatergic inhibition by glycinergic responses in the spinal cord.

Electrophysiological evidence of increased glycine receptor-mediated phasic and tonic inhibition by blockade of glycine transporters in spinal superficial dorsal horn neurons of adult mice

To understand the synaptic and/or extrasynaptic mechanisms underlying pain relief by blockade of glycine transporter subtypes GlyT1 and GlyT2, whole-cell recordings were made from dorsal horn neurons in spinal slices from adult mice, and the effects of NFPS and ALX-1393, selective GlyT1 and GlyT2 inhibitors, respectively, on phasic evoked or miniature glycinergic inhibitory postsynaptic currents (eIPSCs or mIPSCs) were examined. NFPS and ALX-1393 prolonged the decay phase of eIPSCs without affecting their amplitude. In the presence of tetrodotoxin to record mIPSCs, NFPS and ALX-1393 induced a tonic inward current that was reversed by strychnine. Although NFPS had no statistically significant influences on mIPSCs, ALX-1393 significantly increased their frequency. We then further explored the role of GlyTs in the maintenance of glycinergic IPSCs. To facilitate vesicular release of glycine, repetitive high-frequency stimulation (HFS) was applied at 10 Hz for 3 min during continuous recordings of eIPSCs at 0.1 Hz. Prominent suppression of eIPSCs was evident after HFS in the presence of ALX-1393, but not NFPS. Thus, it appears that phasic and tonic inhibition may contribute to the analgesic effects of GlyT inhibitors. However, reduced glycinergic inhibition due to impaired vesicular refilling could hamper the analgesic efficacy of GlyT2 inhibitors.

4-bromopropofol decreases action potential generation in spinal neurons by inducing a glycine receptor-mediated tonic conductance

BACKGROUND AND PURPOSE

Impaired function of spinal strychnine-sensitive glycine receptors gives rise to chronic pain states and movement disorders. Therefore, increased activity of glycine receptors should help to treat such disorders. Although compounds targeting glycine receptors with a high selectivity are lacking, halogenated analogues of propofol have recently been considered as potential candidates. Therefore we asked whether 4-bromopropofol attenuated the excitability of spinal neurons by promoting glycine receptor-dependent inhibition.

EXPERIMENTAL APPROACH

The actions of sub-anaesthetic concentrations of propofol and 4-bromopropofol were investigated in spinal tissue cultures prepared from mice. Drug-induced alterations in action potential firing were monitored by extracellular multi-unit recordings. The effects on GABAA and glycine receptor-mediated inhibition were quantified by whole-cell voltage-clamp recordings.

KEY RESULTS

Low concentrations of 4-bromopropofol (50 nM) reduced action potential activity of ventral horn neurons by about 30%, compared with sham-treated slices. This effect was completely abolished by strychnine (1 μM). In voltage-clamped neurons, 4-bromopropofol activated glycine receptors, generating a tonic current of 65 ± 10 pA, while GABAA - and glycine receptor-mediated synaptic transmission remained unaffected.

CONCLUSIONS AND IMPLICATIONS

The highest glycine levels in the CNS are found in the ventral horn of the spinal cord, a region mediating pain-induced motor reflexes and participating in the control of muscle tone. 4-Bromopropofol may serve as a starting point for the development of non-sedative, non-addictive, muscle relaxants and analgesics to be used to treat low back pain.

Tranexamic acid concentrations associated with human seizures inhibit glycine receptors

Antifibrinolytic drugs are widely used to reduce blood loss during surgery. One serious adverse effect of these drugs is convulsive seizures; however, the mechanisms underlying such seizures remain poorly understood. The antifibrinolytic drugs tranexamic acid (TXA) and ε-aminocaproic acid (EACA) are structurally similar to the inhibitory neurotransmitter glycine. Since reduced function of glycine receptors causes seizures, we hypothesized that TXA and EACA inhibit the activity of glycine receptors. Here we demonstrate that TXA and EACA are competitive antagonists of glycine receptors in mice. We also showed that the general anesthetic isoflurane, and to a lesser extent propofol, reverses TXA inhibition of glycine receptor-mediated current, suggesting that these drugs could potentially be used to treat TXA-induced seizures. Finally, we measured the concentration of TXA in the cerebrospinal fluid (CSF) of patients undergoing major cardiovascular surgery. Surprisingly, peak TXA concentration in the CSF occurred after termination of drug infusion and in one patient coincided with the onset of seizures. Collectively, these results show that concentrations of TXA equivalent to those measured in the CSF of patients inhibited glycine receptors. Furthermore, isoflurane or propofol may prevent or reverse TXA-induced seizures.

Taurine release by astrocytes modulates osmosensitive glycine receptor tone and excitability in the adult supraoptic nucleus

Cells can release the free amino acid taurine through volume-regulated anion channels (VRACs), and it has been hypothesized that taurine released from glial cells is capable of inhibiting action potential (AP) firing by activating neuronal glycine receptors (GlyRs) (Hussy et al., 1997). Although an inhibitory GlyR tone is widely observed in the brain, it remains unknown whether this specifically reflects gliotransmission because most neurons also express VRACs and other endogenous molecules can activate GlyRs. We found that VRACs are absent in neurons of the rat supraoptic nucleus (SON), suggesting that glial cells are the exclusive source of taurine in this nucleus. Application of strychnine to rat hypothalamic explants caused a depolarization of SON neurons associated with a decrease of chloride conductance and could excite these cells in the absence of fast synaptic transmission. This inhibitory GlyR tone was eliminated by pharmacological blockade of VRACs, by cellular taurine depletion, by metabolic inactivation of glia with fluorocitrate, and after retraction of astrocytic processes that intercalate neuronal somata and dendrites. Finally, GlyR tone varied inversely with extracellular fluid tonicity to mediate the osmotic control of AP firing by SON neurons. These findings establish taurine as a physiological gliotransmitter and show that gliotransmission is a spatially constrained process that can be modulated by the morphological rearrangement of astrocytes.

Activation of N-methyl-D-aspartate (NMDA) receptors in the dorsal vagal complex lowers glucose production

Diabetes is characterized by hyperglycemia due partly to increased hepatic glucose production. The hypothalamus regulates hepatic glucose production in rodents. However, it is currently unknown whether other regions of the brain are sufficient in glucose production regulation. The N-methyl-D-aspartate (NMDA) receptor is composed of NR1 and NR2 subunits, which are activated by co-agonist glycine and glutamate or aspartate, respectively. Here we report that direct administration of either co-agonist glycine or NMDA into the dorsal vagal complex (DVC), targeting the nucleus of the solitary tract, lowered glucose production in vivo. Direct infusion of the NMDA receptor blocker MK-801 into the DVC negated the metabolic effect of glycine. To evaluate whether NR1 subunit of the NMDA receptor mediates the effect of glycine, NR1 in the DVC was inhibited by DVC NR1 antagonist 7-chlorokynurenic acid or DVC shRNA-NR1. Pharmacological and molecular inhibition of DVC NR1 negated the metabolic effect of glycine. To evaluate whether the NMDA receptors mediate the effects of NR2 agonist NMDA, DVC NMDA receptors were inhibited by antagonist D-2-amino-5-phosphonovaleric acid (D-APV). DVC D-APV fully negated the ability of DVC NMDA to lower glucose production. Finally, hepatic vagotomy negated the DVC glycine ability to lower glucose production. These findings demonstrate that activation of NR1 and NR2 subunits of the NMDA receptors in the DVC is sufficient to trigger a brain-liver axis to lower glucose production, and suggest that DVC NMDA receptors serve as a therapeutic target for diabetes and obesity.

GABAA and strychnine-sensitive glycine receptors modulate N-methyl-D-aspartate-evoked acetylcholine release from rat spinal motoneurons: a possible role in neuroprotection

Increasing experimental and clinical evidence suggests that abnormal glutamate transmission might play a major role in a vast number of neurological disorders. As a measure of glutamatergic excitation, we have studied the acetylcholine (ACh) release induced by N-methyl-D-aspartate (NMDA) receptor stimulation in primary cultured rat ventral horn spinal neurons and we have evaluated the possibility to limit the consequences of the hyperactivation of glutamatergic receptors, by recruiting the inhibitory transmission mediated by GABA and glycine. For this purpose, we have exposed cell cultures, previously loaded with [(3)H]choline, to NMDA, which increased the spontaneous tritium efflux in a concentration-dependent manner. Tritium release is dependent upon external Ca(2+), tetrodotoxin, Cd(2+) ions and omega-conotoxin GVIA, but not on omega-conotoxin MVIIC nor nifedipine, suggesting the involvement of N-type voltage-sensitive calcium channels. NMDA-mediated [(3)H]ACh release was completely prevented by MK-801, 5,7-diclorokynurenic acid and ifenprodil, while it was strongly inhibited by a lower external pH, suggesting that the involved NMDA receptors contain NR1 and NR2B subunits. Muscimol inhibited NMDA-evoked [(3)H]ACh release and its effect was antagonized by SR95531 and potentiated by diazepam, indicating the involvement of benzodiazepine-sensitive GABA(A) receptors. Also glycine, via strychnine-sensitive receptors, inhibited the effect of NMDA. It is concluded that glutamate acts on the NMDA receptors situated on spinal motoneurons to evoke ACh release, which can be inhibited through the activation of GABA(A) and glycine receptors present on the same neurons. These data suggest that glutamatergic overload of receptors located onto spinal cord motoneurons might be decreased by activating GABA(A) and glycine receptors.

Intrathecal glutamate promotes glycinergic neuronal activity and inhibits the micturition reflex in urethane-anesthetized rats

OBJECTIVES

In order to clarify the role of glutamate in the micturition reflex and in glutamatergic and glycinergic neuronal activity, we examined the effects of intrathecal (IT) injection of glutamate or MK-801 (an N-methyl-D-aspartate receptor antagonist) on bladder activity and on the glutamate and glycine levels in the lumbosacral cord of female rats with or without acute lower thoracic spinal cord injury (SCI).

METHODS

Under urethane anesthesia, isovolumetric cystometry was performed in rats with or without SCI before and after IT injection of glutamate or MK-801 at the lumbosacral cord level. The glutamate and glycine levels of the whole lumbosacral cord were measured after IT injection of glutamate or MK-801 in both groups.

RESULTS

In intact rats, IT glutamate (100 microg) prolonged the interval between bladder contractions and decreased the amplitude of contractions. IT MK-801 (3-100 microg) also prolonged the interval between bladder contractions and decreased the amplitude in intact rats. In SCI rats, cystometry demonstrated the disappearance of bladder contractions, and the glycine level in the lumbosacral cord was elevated. In intact rats, IT glutamate (0.3-100 microg) increased the glycine level in the lumbosacral cord. On the other hand, IT MK-801 (3-100 microg) decreased both glutamate and glycine levels in intact and SCI rats.

CONCLUSIONS

These results suggest that glutamatergic neurons have stimulatory projections to both glutamatergic and glycinergic neurons in the lumbosacral cord, and that glutamatergic neurons inhibit the micturition reflex by stimulating glycinergic neurons.

Receptor-independent actions of cannabinoids on cell membranes: Focus on endocannabinoids

Cannabinoids are a structurally diverse group of mostly lipophilic molecules that bind to cannabinoid receptors. In fact, endogenous cannabinoids (endocannabinoids) are a class of signaling lipids consisting of amides and esters of long-chain polyunsaturated fatty acids. They are synthesized from lipid precursors in plasma membranes via Ca(2+) or G-protein-dependent processes and exhibit cannabinoid-like actions by binding to cannabinoid receptors. However, endocannabinoids can produce effects that are not mediated by these receptors. In pharmacologically relevant concentrations, endocannabinoids modulate the functional properties of voltage-gated ion channels including Ca(2+) channels, Na(+) channels, various types of K(+) channels, and ligand-gated ion channels such as serotonin type 3, nicotinic acetylcholine, and glycine receptors. In addition, modulatory effects of endocannabinoids on other ion-transporting membrane proteins such as transient potential receptor-class channels, gap junctions and transporters for neurotransmitters have also been demonstrated. Furthermore, functional properties of G-protein-coupled receptors for different types of neurotransmitters and neuropeptides are altered by direct actions of endocannabinoids. Although the mechanisms of these effects are currently not clear, it is likely that these direct actions of endocannabinoids are due to their lipophilic structures. These findings indicate that additional molecular targets for endocannabinoids exist and that these targets may represent novel sites for cannabinoids to alter either the excitability of the neurons or the response of the neuronal systems. This review focuses on the results of recent studies indicating that beyond their receptor-mediated effects, endocannabinoids alter the functions of ion channels and other integral membrane proteins directly.

Microdialysis measures of functional increases in ACh release in the hippocampus with and without inclusion of acetylcholinesterase inhibitors in the perfusate

Because brain extracellular acetylcholine (ACh) levels are near detection limits in microdialysis samples, an acetylcholinesterase (AChE) inhibitor such as neostigmine is often added to microdialysis perfusates to increase ACh levels in the dialysate, a practice that raises concerns that the inhibitor might alter the results. Two experiments compared functional differences in ACh release with and without neostigmine. In the first experiment, 30-60% increases in extracellular ACh concentrations in the hippocampus were evident during food-rewarded T-maze training with 20-500 nm neostigmine in the perfusate but no increases were seen without neostigmine. In the second experiment, 78% increases in ACh release in the hippocampus were seen after injections of the GABA(A) receptor antagonist, bicuculline, into medial septum only if neostigmine (50 nm) was included in the perfusate. These findings suggest that, in the hippocampus, endogenous brain AChEs are very efficient at removing extracellular ACh, obscuring differences in ACh release in these experiments. Therefore, inclusion of AChE inhibitors in the microdialysis perfusate may be necessary under some conditions for observations of functional changes in release of ACh in the hippocampus.

Δ9-Tetrahydrocannabinol and Endogenous Cannabinoid Anandamide Directly Potentiate the Function of Glycine Receptors

Anandamide (AEA) and delta9-tetrahydrocannabinol (THC) are endogenous and exogenous ligands, respectively, for cannabinoid receptors. Whereas most of the pharmacological actions of cannabinoids are mediated by CB1 receptors, there is also evidence that these compounds can produce effects that are not mediated by the activation of identified cannabinoid receptors. Here, we report that THC and AEA, in a CB1 receptor-independent manner, cause a significant potentiation of the amplitudes of glycine-activated currents (I(Gly)) in acutely isolated neurons from rat ventral tegmental area (VTA) and in Xenopus laevis oocytes expressing human homomeric (alpha1) and heteromeric (alpha1beta1) subunits of glycine receptors (GlyRs). The potentiation of I(Gly) by THC and AEA is concentration-dependent, with respective EC50 values of 86 +/- 9 and 319 +/- 31 nM for alpha1 homomeric receptors, 73 +/- 8 and 318 +/- 24 nM for alpha1beta1 heteromeric receptors, and 115 +/- 13 and 230 +/- 29 nM for native GlyRs in VTA neurons. The effects of THC and AEA are selective for I(Gly), because GABA-activated current in VTA neurons or in X. laevis oocytes expressing alpha2beta3gamma2 GABA(A) receptor subunits were unaffected by these compounds. The maximal potentiation by THC and AEA was observed at the lowest concentration of glycine; with increasing concentrations of glycine, the potentiation significantly decreased. The site for THC and AEA seems to be distinct from that of the alcohol and volatile anesthetics. The results indicate that THC and AEA, in pharmacologically relevant concentrations, directly potentiate the function of GlyRs through an allosteric mechanism.

RNA editing produces glycine receptor alpha3(P185L), resulting in high agonist potency

The function of supramedullary glycine receptors (GlyRs) is still unclear. Using Wistar rat collicular slices, we demonstrate GlyR-mediated inhibition of spike discharge elicited by low glycine (10 microM). Searching for the molecular basis of this phenomenon, we identified a new GlyR isoform. GlyR alpha3(P185L), a result of cytidine 554 deamination, confers high glycine sensitivity (EC50 approximately 5 microM) to neurons and thereby promotes the generation of sustained chloride conductances associated with tonic inhibition. The level of GlyR alpha3-C554U RNA editing is sensitive to experimentally induced brain lesion, inhibition of cytidine deamination by zebularine and inhibition of mRNA transcription by actinomycin D, but not to blockade of protein synthesis by cycloheximide. Conditional regulation of GlyR alpha3(P185L) is thus likely to be part of a post-transcriptional adaptive mechanism in neurons with enhanced excitability.

Excised porcine skin experimental systems to validate quantitative microdialysis methods for determination of drugs in skin after topical application

Microdialysis is useful as a method to evaluate the disposition of drugs in the skin to design improved transdermal delivery systems (TDDSs). In this study, quantitative microdialysis methods were validated in excised porcine skin experimental systems in vitro. Flurbiprofen (FP), used as a model drug, showed high affinity for the skin tissues in equilibrium states between the medium and skin. The membrane clearances of FP for permeation through the membrane of a dialysis fiber placed in the skin (CL(m in S)) were lower than that in the medium. The adsorption of components in the skin to the membrane surface of the dialysis fiber and accumulation of FP near the dialysis fiber are the most likely reasons for this. When CL(m in S) was used to predict the extracellular FP concentration in skin (C(T)), the value obtained was lower than that expected from the FP concentration in the medium on the dermis side, which should be equal to C(T) at equilibrium. In the zero net flux (ZNF) method, in which the concentration difference of perfusate (DeltaC) between the inflow and outflow were used to obtain C(T), the predicted C(T) was similar to the expected value. In an in vitro skin permeation experiment, the ZNF method was used for the prediction of C(T) near the dialysis fiber. The predicted C(T) was over 10 times higher than the FP concentration in the medium on the dermis side, suggesting a concentration gradient in the dermis. Although the ZNF method is good for predicting the C(T) in skin, the mass balance has to be considered for the quantitative evaluation of the skin permeation of drugs. In this study, the effect of the mass transfer of FP from the perfusate to the skin on the cumulative amount of FP passing through the skin was relatively low because of the use of suitable solutions as perfusate. The perfusion conditions and schedules should be designed carefully for quantitative evaluations using the ZNF method. These results provide useful information for the in vivo application of quantitative microdialysis to evaluate TDDS.

Role of glial and neuronal glycine transporters in the control of glycinergic and glutamatergic synaptic transmission in lamina X of the rat spinal cord

Using whole cell voltage clamp recordings from lamina X neurones in rat spinal cord slices, we investigated the effect of glycine transporter (GlyT) antagonists on both glycinergic inhibitory postsynaptic current (IPSCs) and glutamatergic excitatory postsynaptic current (EPSCs). We used ORG 24598 and ORG 25543, selective antagonists of the glial GlyT (GlyT1) and neuronal GlyT (GlyT2), respectively. In rats (P12-P16) and in the presence of kynurenic acid, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and bicuculline, ORG 24598 and ORG 25543 applied individually at a concentration of 10 microm induced a mean inward current of -10/-50 pA at -60 mV and increased significantly the decay time constants of miniature (mIPSCs), spontaneous (sIPSCs) and electrically evoked glycinergic (eIPSCs) inhibitory postsynaptic currents. ORG 25543, but not ORG 24598, decreased the frequency of mIPSCs and sIPSCs. Replacing extracellular sodium with N-methyl-d-glucamine or superfusing the slice with micromolar concentrations of glycine also increased the decay time constant of glycinergic IPSCs. By contrast, the decay time constant, amplitude and frequency of miniature GABAergic IPSCs recorded in the presence of strychnine were not affected by ORG 24598 and ORG 25543. In the presence of strychnine, bicuculline and CNQX, we recorded electrically evoked NMDA receptor-mediated EPSCs (eEPSCs). eEPSCs were suppressed by 30 micromd-2-amino-5-phosphonovalerate (APV), an antagonist of the NMDA receptor, and by 30 microm dichlorokynurenic acid (DCKA), an antagonist of the glycine site of the NMDA receptor. Glycine (1-5 microm) and d-serine (10 microm) increased the amplitude of eEPSCs whereas l-serine had no effect. ORG 24598 and ORG 25543 increased significantly the amplitude of NMDA receptor-mediated eEPSCs without affecting the amplitude of non-NMDA receptor-mediated eEPSCs. We conclude that blocking glial and/or neuronal glycine transporters increased the level of glycine in spinal cord slices, which in turn prolonged the duration of glycinergic synaptic current and potentiated the NMDA-mediated synaptic response.

Positive N-methyl-d-aspartate receptor modulation by selective glycine transporter-1 inhibition in the rat dorsal spinal cord in vivo

In this study we have employed the selective glycine transporter-1 (GlyT-1) and GlyT-2 transporter inhibitors R-(-)-N-methyl-N-[3-[(4-trifluoromethyl)phenoxy]-3-phenyl-propyl]glycine (1:1) lithium salt (Org 24598) and 4-benzyloxy-3,5-dimethoxy-N-[1-(dimethylaminocyclopently)methyl]benzamide (Org 25543), respectively, and microdialysis perfusion to determine the effect of GlyT transporter inhibition on extracellular amino acid concentrations in the lumbar dorsal spinal cord of the halothane-anaesthetised rat. Reverse dialysis of Org 24598 (0.1-10 microM) induced a concentration-related increase in extracellular glycine accompanied by a progressive increase in citrulline, but not aspartate, glutamate or GABA, efflux. Org 25543 (10 microM) by the same route induced a similar increase in glycine levels without affecting the efflux of other amino acids quantified. To test the hypothesis that the increase in citrulline efflux resulted from activation of the N-methyl-D-aspartate receptor (NMDA-R)/nitric oxide synthase (NOS) signalling cascade, the sensitivity was determined of GlyT-1 inhibition-induced effects to NMDA-R antagonism or NOS inhibition. Co-administration by reverse dialysis of the selective NMDA-R channel blocker MK-801 (0.5 mM) or the selective antagonist of the strychnine-insensitive glycine site, 7-chlorokynurenic acid (1 mM), with Org 24598 (10 microM) did not affect the uptake inhibition-induced increase in glycine efflux, but did significantly attenuate the increase in extracellular citrulline. Similarly, co-administration with Org 24598 of the isoform non-selective and selective neuronal NOS inhibitors Nomega-nitro-L-arginine methyl ester (1 mM) or 1-(2-trifluoromethylphenyl)imidazole (0.2 mM), respectively, prevented Org 24598-induced citrulline efflux with no effect on increased glycine efflux. These data provide evidence that the observed increased in extracellular citrulline is a consequence of positive modulation of NMDA-R, secondary to increased extracellular glycine and support a protective role for GlyT-1 against fluctuations in extracellular glycine uptake at glutamatergic synapses in the dorsal spinal cord. Such a mechanism could be important to NMDA-R-mediated synaptic plasticity in the spinal cord and be of relevance to the clinical usage of GlyT-1 inhibitors.

Effect of glycerol-induced acute renal failure on the pharmacokinetics of lidocaine after transdermal application in rats

In this study, the effect of glycerol-induced acute renal failure (ARF) on the pharmacokinetics of lidocaine after transdermal application was investigated in rats. Microdialysis method was applied in vitro and in vivo to the abdominal skin of rats. After topical application of 1% lidocaine, the cumulative amount of lidocaine permeated through the excised rat abdominal skin showed parallel effect between normal and ARF rats with no significant difference in the in vitro permeability coefficient of lidocaine between them, while area under the plasma concentration versus time curve of lidocaine in ARF rats increased significantly. The protein binding rate of lidocaine in ARF plasma and the blood vessel permeability to muscle tissues, assessed by beta-D-glucopyranosyl fluorescein isothiocyanate-labeled (FITC) albumin, increased significantly. After intravenous infusion of 5 mg/h/kg lidocaine, both of the total body clearance and the volume of distribution of lidocaine in the ARF rats decreased significantly. These results suggested that renal dysfunction did not have any effect on the skin permeability of lidocaine, but might change the plasma protein binding of drug and blood vessel permeability which led to high plasma concentration of lidocaine.