Activation of the RAS/B-RAF-MEK-ERK pathway in satellite glial cells contributes to substance p-mediated orofacial pain.

The cross talk between trigeminal ganglion (TG) neurons and satellite glial cells (SGCs) is crucial for the regulation of inflammatory orofacial pain. Substance P (SP) plays an important role by activating neurokinin (NK)-I receptors in this cross talk. The activation of extracellular signal-regulated kinase (ERK) 1/2, protein kinase A (PKA) and protein kinase C (PKC) in neurons and SGCs of peripheral ganglions by peripheral inflammation is associated with inflammatory hypersensitivity. This study tested the hypothesis that SP evoked SP-NK-I receptor positive feedback via the Renin-Angiotensin System/B-Protein Kinase A-Rapidly Accelerates Fibrosarcoma-MEK-Extracellular Signal-Regulated Kinase (RAS/PKA-RAF-MEK-ERK) pathway, which is involved in pain hypersensitivity. Inflammatory models were induced in vivo by injecting Complete Freund's adjuvant (CFA) into the whisker pad of rats. SP was administrated to SGCs in vitro for investigating, whether SP regulates the expression of NK-I receptor in the SGC nucleus. The effects of RAS-RAF-MEK, PKA and PKC pathways in this process were measured by co-incubating SGCs with respective Raf, PKA, PKC and MEK inhibitors in vitro and by pre-injecting these inhibitors into the TG in vivo. SP significantly upregulated NK-I receptor, p-ERK1/2, Ras, B-Raf, PKA and PKC in SGCs under inflammatory conditions. In addition, L703,606 (NK-I receptor antagonist), U0126 (MEK inhibitor), Sorafenib (Raf inhibitor) and H892HCL (PKA inhibitor) but not chelerythrine chloride (PKC inhibitor) significantly decreased NK-I mRNA and protein levels induced by SP. The allodynia-related behavior evoked by CFA was inhibited by pre-injection of L703,606, U0126, Sorafenib and H892HCL into the TG. Overall, SP upregulates NK-I receptor in TG SGCs via PKA/RAS-RAF-MEK-ERK pathway activation, contributing to a positive feedback of SP-NK-I receptor in inflammatory orofacial pain.

P2Y14 receptor is functionally expressed in satellite glial cells and mediates interleukin-1ß and chemokine CCL2 secretion.

Satellite glial cells (SGCs) activation in the trigeminal ganglia (TG) is critical in various abnormal orofacial sensation in nerve injury and inflammatory conditions. SGCs express several subtypes of P2 purinergic receptors contributing to the initiation and maintenance of neuropathic pain. The P2Y14 receptor, a G-protein-coupled receptor activated by uridine diphosphate (UDP)-glucose and other UDP sugars, mediates various physiologic events such as immune, inflammation, and pain. However, the expression, distribution, and function of P2Y14 receptor in SGCs remains largely unexplored. Our study reported the expression and functional identification of P2Y14 receptor in SGCs. SGCs were isolated from TG of rat, and the P2Y14 receptor expression was examined using immunofluorescence technique. Cell proliferation and viability were examined via cell counting kit-8 experiment. Immunofluorescence demonstrated the presence of P2Y14 receptor in SGCs. Immunofluorescence and western blot showed that UDP-glucose treatment upregulated glial fibrillary acid protein, a common marker for glial activation. Extracellular UDP-glucose enhanced the phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38, which were both abolished by the P2Y14 receptor inhibitor (PPTN). Furthermore, quantitative reverse transcription polymerase chain reaction and enzyme-linked immunosorbent assay demonstrated that extracellular UDP-glucose significantly enhanced interleukin-1ß (IL-1ß) and chemokine CCL2 (CCL2) release, which was abolished by PPTN and significantly decreased by inhibitors of MEK/ERK (U0126) and p38 (SB202190). Our findings directly proved the functional presence of P2Y14 receptor in SGCs. It was also verified that P2Y14 receptor activation was involved in activating SGCs, phosphorylating MAPKs, and promoting the secretion of IL-1ß and CCL2 via ERK and p38 pathway.

Effect of Titanium Particles on the Voltage-Gated Potassium Channel Currents in Trigeminal Root Ganglion Neurons.

PURPOSE: Titanium (Ti) is the key material used in dental implants because of its excellent biocompatibility. But wear and corrosion Ti particles had been widely reported to induce inflammation and promote bone absorption. However, little information is known about the damage of Ti particles on neurons. MATERIALS AND METHODS: Trigeminal root ganglion (TRG) neurons were exposed to Ti particles (<5 µm). The electrophysiological properties of 2 main subtypes of voltage-gated potassium channels (VGPCs) (KA and KV) were examined by whole-cell patch-clamp techniques. RESULT: With the presence of 0.25 mg/mL Ti particles, amplitudes of IK, A and IK, V were both obviously inhibited. For IK, A, the activation V1/2 shifted to the depolarizing direction with an increased k value, whereas the inactivation V1/2 showed obvious hyperdepolarizing shifts. For IK, V, 0.5 mg/mL Ti particles produced a depolarizing shift of activation V1/2 with a slower activation rate. No significant changes of its inactivation kinetics were found. CONCLUSION: Titanium (Ti) particles might alter the electrophysiological properties of VGPCs on TRG neurons, which are likely to further influence the excitability of neurons.

[Xylazine Produced Analgesic Effect via Inhibits Hyperpolarization-activated Cyclic Nucleotide-gated Ion Channels Currents].

OBJECTIVE: To investigate the analgesic mechanism of xylazine by inhibiting the activation of hyperpolarized cyclic nucleotide-gated (HCN) ion channels. METHODS: HCN subchannel 1 (HCN1) knockout mice (HCN1-/-) and HCN1 wild type mice (HCN1+/+) were intraperitoneally injected with physiological saline and xylazine (10, 20, 30, and 40 mg/kg). Mechanical pain test and tail flick test were used to test the analgesic effect of xylazine by using the percentage of the maximal possible effect (%MPE); The control group and test groups of different concentrations of xylazine (12.5, 25, 50, and 100 µmol/L) were set up using HEK 293 cells transfected HCN1 plasmid and HCN subchannel 2 (HCN2) plasmid, respectively. The activated current of hyperpolarized HEK 293 cells expressing HCN1 and HCN2 ion channels and the inhibition rate of xylazine on hyperpolarization-activated currents were recorded using a whole cell patch clamp. RESULTS: The results demonstrated that %MPE of the mechanical pain stimuli test and the thermal radiation stimuli test increased with the higher concentration of xylazine injected for both HCN1+/+ mice and HCN1-/-mice. When injecting xylazine by 30 mg/kg and 40 mg/kg, the %MPE of mechanical pain stimuli test for HCN1-/- mice were %MPE= (62.06±14.72) % and %MPE= (69.92±16.09) %, respectively; and the percentages of tail flick tests were (52.50±1.97) % and %MPE= (64.74±6.34) %, respectively. But for HCN1+/+ mice, the percentages of mechanical pain stimuli test were %MPE= (75.47±8.06) % and %MPE= (86.35±11.31) %; respectively, and the percentage of tail flick tests were %MPE= (57.83±4.82) % and (74.98±9.35) %. The analgesic effect results of the mechanical pain test and tail flick test of HCN1+/+ mice were significantly different from HCN1-/- mice ( P<0.05). Whole-cell patch clamp test results showed that xylazine had inhibitory effects on the currents of HCN1 and HCN2 ion channels, and the hyperpolarization-activated currents inhibition rate of HCN1 by xylazine (12.5-100 µmol/L) was between (24.62±23.62) %- (62.40±15.48) %; V1/2 of HCN1 was between (-79.58±1.56) mV- (-98.95±3.57) mV. The Ih inhibition rate of HCN2 by xylazine (12.5-100 µmol/L) was between (29.19±17.82) %- (80.02±6.64) %; with V1/2 of HCN2 between (-102.17±1.36) mV- (-117.48±2.38) mV. CONCLUSION: Xylazine showed better analgesic effect on HCN1+/+ mice than HCN1-/- mice. Xylazine can produce analgesic effect by inhibiting HCN ion channel currents.

OECs transplantation results in neuropathic pain associated with BDNF regulating ERK activity in rats following cord hemisection.

BACKGROUND: The olfactory ensheathing cells (OECs) derived from olfactory bulb (OB) may improve motor function after transplantation in injured spinal cord. However, the effects of OEC transplantation on sensory function have not been reported yet. The purpose of this study is to investigate whether OEC transplantation could affect the sensory function and to analyze the underlying mechanism. RESULTS: OEC transplantation into the hemisected spinal cords can result in hyperalgesia, indicated by radiant and mechanical stimuli towards the plantar surface in rats. This could be associated with upregulation of Brain Derived Neurotrophic Factor (BDNF), indicated by RT-PCR. Immunofluorecent staining showed that BDNF was mainly located in the neurons of the laminas I and II of the dorsal horn. Moreover, a notable upregulation on the level of p-ERK (phosphorylation of extracellular signal-regulated kinase), the downstream molecule of BDNF, was detected by using Western Blot. These findings indicate that the increased BDNF level associated with the p-ERK was possibly involved in neuropathic pain in hemisected spinal cord subjected to OEC transplantation. CONCLUSIONS: The transplantation of OECs may induce the noticeable pain hypersensitivity in rats after hemisected spinal cord injury, and the possible mechanism may be associated with the phosphorylation of ERK and the activated BDNF overexpression.

The P2Y14 receptor in the trigeminal ganglion contributes to the maintenance of inflammatory pain.

P2Y purinergic receptors expressed in neurons and satellite glial cells (SGCs) of the trigeminal ganglion (TG) contribute to inflammatory and neuropathic pain. P2Y14 receptor expression is reported in the spinal cord, dorsal root ganglion (DRG), and TG. In present study, the role of P2Y14 receptor in the TG in inflammatory orofacial pain of Sprague-Dawley (SD) rats was investigated. Peripheral injection of complete Freund's adjuvant (CFA) induced mechanical hyperalgesia with the rapid upregulation of P2Y14 receptor, glial fibrillary acidic protein (GFAP), interleukin-1ß (IL-1ß), tumor necrosis factor-α (TNF-α), C-C chemokine CCL2, phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2), and phosphorylated p38 (p-p38) proteins in the TG. Furthermore, immunofluorescence staining confirmed the CFA-induced upregulation of P2Y14 receptor. Double immunostaining showed that P2Y14 receptor colocalized with glutamine synthetase (GS) and neuronal nuclei (NeuN). Finally, trigeminal injection of a selective antagonist (PPTN) of P2Y14 receptor attenuated CFA-induced mechanical hyperalgesia. PPTN also decreased the upregulation of the GFAP, IL-1ß, TNF-α, CCL2, p-ERK1/2, and p-p38 proteins. Our findings showed that P2Y14 receptor in TG may contribute to orofacial inflammatory pain via regulating SGCs activation, releasing cytokines (IL-1ß, TNF-α, and CCL2), and phosphorylating ERK1/2 and p38.

FMRFamide modulates outward potassium currents in mouse olfactory sensory neurons.

1. The olfactory system can detect the presence of low concentrations of odourant molecules and discriminate even slight differences among molecules with a very similar chemical structure. The detection and discrimination of odourants are correlated with the electrophysiology of the olfactory sensory neurons. To get a better understanding of the molecular mechanisms of olfactory transduction, it is therefore of considerable importance to obtain electrophysiological recordings of olfactory sensory neurons. FMRFamide (Phe-Met-Arg-Phe-NH(2)), secreted from the nerve terminals of the nasal cavity, has been suggested to act as a neurotransmitter or neuromodulator, playing an important role in modulating the activity of olfactory receptor neurons. Its effects on voltage-dependent potassium currents in the mouse olfactory sensory neurons were investigated in the present study using the whole-cell patch-clamp technique. 2. Olfactory sensory neurons were isolated from the Kunming Mouse (KM) mouse olfactory epithelium. Different protocols were applied to obtain delayed-rectifier potassium current (I(K)) and fast transient potassium current (I(A)). The effects of FMRFamide on the outward potassium currents, including I(K) and I(A), in mouse olfactory sensory neurons were investigated. 3. We found that FMRFamide (5 micromol/L) increased the magnitude of I(K). However no effect on I(A) was observed. The activation dynamics of both currents were not changed by FMRFamide. 4. In conclusion, FMRFamide may play a role in the modulation of peripheral olfactory signals by regulating I(K). This modulation may shorten the phase of the fast repolarization of the action potential in mouse olfactory sensory neurons and increase the excitability of the neuronal membrane.

[Mechanism of potassium channel in hypoxia-ischemic brain edema: experiment with neonatal rat astrocyte].

OBJECTIVE: To investigate the mechanism of potassium channel in brain edema caused by hypoxia-ischemia (HI). METHODS: Astrocytes were obtained from 3-day-old SD rats, cultured, and randomly divided into 2 groups: normoxia group, cultured under normoxic condition, and hypoxic-ischemic group, cultured under hypoxic-ischemic condition. The cell volume was measured by radiologic method. Patch-clamp technique was used to observe the electric physiological properties of the voltage-gated potassium channels (Kv) in a whole cell configuration, and the change of voltage-gated potassium channel current (IKv) was recorded in cultured neonatal rat astrocyte during HI. Aquaporin 4 (AQP4) expression vector was constructed from pSUPER vector and transfected into the astrocytes (AQP4 RNAi) to construct AQP4 knockdown (AQP4-/-) cells. cellular volume was determined using [3H]-3-O-methyl-D-glucose uptake in both AQP4-/- and AQP4+/+ cells under the condition of HI. Real time PCR and Western blotting were used to detect the mRNA and protein expression of AQP4. RESULTS: The percentages of the AQP4+/+ and AQP4-/- astrocyte volumes in the condition of HI for 0.5, 1, 2, and 4 h were 104+/-7, 109+/-6, 126+/-12, and 152+/-9 times, and 97+/-7, 105+/-9, 109+/-7, and 132+/-6 times as those of their corresponding control groups (all P<0.05), thus showing that the cellular volume of both AQP4+/+ and AQP4-/- astrocytes significantly increased during HI and the degrees of edema mediated by AQP4 knockdown at different time points were all significantly milder (all P<0.05). The current density values at the time points 0.5, 1, 2, and 4 h of the HI group were 107+/-9, 91+/-10, 76+/-6, 37+/-11, respectively, compared to that of the control group of 116+/-8, showing a tendency of time-dependent decreasing manner (all P<0.05). CONCLUSION: During HI, the downregulation of outward potassium (K+) conductance may prevent the emission of intracellularly accumulated K+ ions, thus resulting in osmotically derived water influx into astrocytes via aquaporin-4 and then cell swelling.

[Mixed enzyme applied to develop the method on BAlb/c mouse Kupffer cell isolated and cultured in vitro].

OBJECTIVE: To research the reliable method for the isolation and culture of Kupffer cell in BALB/c mouse by mixed enzyme. METHODS: Kupffer cells were isolated from liver by in situ perfusion and digestion with 0.1% IV collagenase, 0.2% pronase and 0.01% Dnase I, and by percoll density gradient centrifugation. Kupffer cells were identified by fluorescence microscope, immunohistochemistry and cell endocytosis effect. RESULTS: Kupffer cells were isolated successfully with high purity, the yield of (2-3) 10(6)/per mouse liver and the identification that 0.4% trypan blue indicated that the cells survival rate and purity were more than 96% and more than 92% respectively. The shape of Kupffer cell appeared to be multiplicity, irregularity, polygon and multiangular. Kupffer cells showed lysozyme positive by immunohistochemistry staining. And particles of India ink were found in cytoplasm. CONCLUSION: Here described technique for isolation and culture of Kupffer cells is simple and reliable, and can be used for preparing Kupffer cells with high yield, activity and purity.

[Effect of levetiracetam on the sodium currents of rat hippocampal neurons exposed to coriaria lactone].

OBJECTIVE: To test the effect of Levetiracetam (LEV) on the sodium currents of rat hippocampal neurons exposed to epileptogenic coriaria lactone (CL). METHODS: Acutely isolated Sprague-Dawley Rat hippocampal neurons were subjected to the whole-cell mode of patch clamp under experimental conditions designed to detect voltage-gated sodium currents. The CL (0.2 mg/mL) was used to increase the sodium currents of the neurons. Then the LEV was added (150 or 300 micromol/L) to test the effect of LEV on the peak current amplitudes through a comparison with the control group in which extracellular solution was added instead and the group in which nothing was added. Another. group was pretreated with 300 micromol/L of LEV before the neutrons were treated with the CL. RESULTS: The maximum peak amplitudes (MPA) of the sodium currents increased 36.92% +/- 2.84% by the 150 micromol/L of LEV (P < 0.05), similar to those exposed to the CL only (P > 0.05). The increase of MPA of the sodium currents by the 300 micromol/L of LEV (16.58% +/- 1.56%) was less than those exposed to the CL only (P < 0.05). However, no significant difference was found between the 300 micromol/L LEV treated group and the control group (P > 0.05). The MPA of the sodium currents of LEV pretreated neutrons increased 32.86% +/- 6.73% (P < 0.05), similar to those without pretreatment (P > 0.05). CONCLUSION: The LEV does not decrease the sodium currents of rat hippocampal neurons induced by the CL. The antiepileptic action of LEV has nothing to do with the neuronal voltage-gated sodium channels.

[Effects of coriaria lactone on the sodium currents of actuely isolated rat hippocampal neurons].

OBJECTIVE: The present study tried to find out the effects of coriaria lactone (CL) on the sodium currents of the rat hippocampal neurons and their significance. METHODS: The sodium currents of the acutely isolated Sprague-Dawley rat hippocampal neurons were recorded by employing the patch-clamp technique in the whole-cell voltage-clamp mode. The effects of CL on the peak currents in the neuron membrane were assessed and analyzed. RESULTS: Both 0.1 mg/mL and 0.2 mg/mL CL increased the maximal peak density of sodium currents significantly (17.32%+/-8.52% vs 37.98%+/-4.91%). The effect of 0.2 mg/mL CL (P < 0.05) was more significant than that of 0.1 mg/mL CL (P > 0.05), when compared with the control (3.16%+/-0.65%). CONCLUSION: CL can increase the amplitudes of the voltage-dependent sodium currents in the acutely isolated hippocampal neurons. This effect may contribute to the enhanced excitability of hippocampal neurons and play a role in the epileptogenetic process of CL.

[The feasibility exploration of cultured newborn rat ventricular myocyte taking the place of acutely enzymatic isolated myocardium for study in electrophysiology of pacemaker current].

OBJECTIVE: To investigate the feasibility of cultured rat ventricular myocytes taking the place of acutely enzymatic isolated myocardia for study in the pacemaker current electrophysiology. METHODS: By using patch-clamp technique, the whole-cell pacemaker currents were recorded to study the difference of pacemaker current electrophysiology between neonatal rat ventricular myocytes isolated acutely and maintained in cell culture. RESULTS: The cell membrane capacitances (Cm) were significantly decreased in myocardia even upon short term of cell culture. The Cm of myocardia cultured 1-3 day were (43 +/- 3) pF, with decreased 23% compared to acute enzymatic isolated cells C(56+/-7) pF, P<0. 013. It seemed like the Cm increased slightly upon cell cultured time, but no significant difference appearing among various culture stages (P > 0. 05) . No significant difference of pacemaker current electrophysiological character, such as reverse potential, current density, active threshold and V0.5, was detected from different cell group (P>0. 05). CONCLUSION: The cultured myocardium can take place of acute enzymatic isolated myocardium used to study in pacemaker current. The cells cultured no more than one week may be more suitable to this kind of electrophysiological experiment.

[Acute isolation and identification of cerebral neurons from the late third instar larvae of Drosophila melanogaster].

OBJECTIVES: To develop a new method for acute isolation of the cerebral neurons from late third instar larvae of Drosophila melanogaster. METHODS: The dissociated cells were characterized by morphological observation and whole-cell voltage-clamp recording. The brains were dissected from late third instar larvae, torn into small fragments, and then were digested in the calcium-magnesium-free PBS solution endowed with collagenase for 45-60 minutes. Single cell was obtained by micro-shaking the digested fragments for 5 to 10 s until the clumps of the tissue were not invisible. Preparation of dispersed cells was incubated in the culture media of Drosophila for thirty minutes at room temperature (20 +/- 1) degrees C. RESULTS: All neurons studied were categorized into three types according to morphological observation: large (> 8 microm) round type I neuroblast-like cells (7%), small (2-5 microm) type II cells (77%). and intermediate-sized type II cells (16%). Neurogliocytes were not found. The electrophysiological properties of three types of neurons were investigated by whole-cell voltage-clamp recording technique. Five types of outward potassium currents were detected readily. CONCLUSION: Morphological and electrophysiological investigation showed that the method for acute isolation of Drosophila neurons is simple, available and stable.

The effect of gliquidone on KATP channels in pancreatic ß-cells, cardiomyocytes, and vascular smooth muscle cells.

AIMS: Sulfonylurea drugs exert an insulinotropic effect through ATP-sensitive potassium (KATP) channel inhibition in pancreatic islet cells. These channels are also expressed in cardiomyocytes and vascular smooth muscle cells (VSMCs), suggesting potential for adverse cardiovascular effects. We evaluated the effects of Gliquidone (Glq) on sulfonylurea receptors in HIT-T15 cells (SUR1), cardiomyocytes (SUR2A), and VSMCs (SUR2B). METHODS: The concentration-dependent effects of Glq (0.001-500 µM) on KATP channels were assessed using whole-cell patch clamp in HIT-T15 cells, rat cardiomyocytes, and VSMCs. Parallel studies using Glibenclamide (Glb) (0.001-10 µM) and Gliclazide (Glc) (0.01-500 µM)were conducted as controls. RESULTS: In HIT-T15 cells, Glb exhibited the lowest IC50 (0.03 µM), as compared to Glq (0.45µM) and Glc (1.21µM). However, Glq had higher IC50 in cardiomyoctes and VSMCs, as compared to Glb (119.1 vs. 0.01 and 149.7 vs. 0.09 µM, respectively), suggesting that Glq is more selective to ß-cells than Glb. Thus, Glq may have fewer side effects in cardiomyoctes and VSMCs. CONCLUSIONS: Glq is a highly selective SUR secretagogue with moderate affinity to ß-cells, but low affinity to cardiomyocytes and VSMCs. Our data also reveal the non-selective nature of Glb, as evidenced by high binding affinity to KATP channels in all the three cell types examined.

The common anesthetic, sevoflurane, induces apoptosis in A549 lung alveolar epithelial cells.

Lung alveolar epithelial cells are the first barrier exposed to volatile anesthetics, such as sevoflurane, prior to reaching the targeted neuronal cells. Previously, the effects of volatile anesthetics on lung surfactant were studied primarily with physicochemical models and there has been little experimental data from cell cultures. Therefore it was investigated whether sevoflurane induces apoptosis of A549 lung epithelial cells. A549 cells were exposed to sevoflurane via a calibrated vaporizer with a 2 l/min flow in a gas­tight chamber at 37˚C. The concentration of sevoflurane in Dulbecco's modified Eagle's medium was detected with gas chromatography. Untreated cells and cells treated with 2 µM daunorubicin hydrochloride (DRB) were used as negative and positive controls, respectively. Apoptosis factors, including the level of ATP, apoptotic­bodies by terminal deoxynucleotidyl transferase­mediated dUTP nick end labeling (TUNEL) assay, DNA damage and the level of caspase 3/7 were analyzed. Cells treated with sevoflurane showed a significant reduction in ATP compared with untreated cells. Effects in the DRB group were greater than in the sevoflurane group. The difference of TUNEL staining between the sevoflurane and untreated groups was statistically significant. DNA degradation was observed in the sevoflurane and DRB groups, however this was not observed in the untreated group. The sevoflurane and DRB groups induced increased caspase 3/7 activation compared with untreated cells. These results suggest that sevoflurane induces apoptosis in A549 cells. In conclusion, 5% sevoflurane induced apoptosis of A549 lung alveolar epithelial cells, which resulted in decreased cell viability, increased apoptotic bodies, impaired DNA integrality and increased levels of caspase 3/7.

Inhibition of voltage-gated sodium channels by emulsified isoflurane may contribute to its subarachnoid anesthetic effect in beagle dogs.

BACKGROUND: Volatile anesthetics, in addition to their general anesthesia action, have been proven to produce regional anesthetic effect in various animal models. The major aim of this study was to examine whether emulsified isoflurane (EI) could also produce subarachnoid anesthesia and to investigate its possible mechanism. METHODS: Beagle dogs were randomly assigned into 5 groups (n = 6/group): intrathecally receiving 1% lidocaine 0.1 mL/kg, 30% intralipid 0.1 mL/kg (control), or 8% EI at doses of 0.05, 0.075, or 0.1 mL/kg, respectively. Consciousness state, motor function of limbs, and response to nociceptive stimulus were observed after drug administration. The effect of EI on voltage-gated Na channel was recorded from isolated spinal neurons of rats, using the whole-cell patch-clamp technique. Inhibition of peak sodium currents and effect of EI on Na channel gating were analyzed. RESULTS: Emulsified isoflurane produced subarachnoid anesthesia in a dose-dependent manner, and at the dose of 0.1 mL/kg, the effect of 8% EI was similar to 1% lidocaine. Sodium channel currents were inhibited by EI at clinically relevant concentrations, with the IC50 (median inhibitory concentration) at 0.69 ± 0.08 mM. Voltage activation of Na channels was positive, shifted by isoflurane at the concentration of 0.77 mM, and V½ of activation (voltage for half-maximal activation) shifted from -12.4 ± 2.7 mV to -7.3 ± 2.3 mV (P < 0.01). CONCLUSIONS: Emulsified isoflurane produced dose-dependent subarachnoid anesthesia, and this effect might be mediated by inhibition of EI on voltage-gated Na channels in the spinal cord.

Remifentanil induces L-type Ca2+ channel inhibition in human mesenteric arterial smooth muscle cells.

PURPOSE: Remifentanil is known to cause vasodilation at standard anesthetic concentrations. The intracellular mechanisms underlying its vasodilator action may involve the activation of ion channels. The purpose of this study was to examine whether remifentanil inhibits L-type calcium channels (Ca.(L)) and provides dose-dependent effects on L-type calcium channel Ba(2+) currents (I(Ba.L)) in human mesenteric arterial smooth muscle cells. METHODS: Using the whole-cell patch-clamp method, an in depth analysis of the mechanism of the I(Ba.L) induced by remifentanil was performed in cells which were enzymatically isolated from human mesenteric arterial smooth muscle. Ten millimolars Ba(2+) was used to replace 1.5 mM Ca(2+) to increase the amplitude of the inward current through Ca(2+)channels. L-type calcium channel Ba(2+) was elicited during 50 msec depolarizing test pulses (150 msec duration) to +80 mV (10 mV increments) from a holding potential of -60 mV. The effects of remifentanil on Ca.(L) were observed at the following concentrations: 1.21, 4.84, and 19.4 nmol.L(-1) and were compared with control. RESULTS: Remifentanil produced a concentration-dependent block of I(Ba,L) with IC(50) values of 38.90 +/- 3.96 x 10(-3) micromol.L(-1). The L-type calcium channel blocker, nifedipine, antagonized these remifentanil-induced currents. Remifentanil, at all concentrations, shifted the maximum of the current-voltage relationship in the hyperpolarizing direction of I(Ba.L). CONCLUSION: Remifentanil significantly inhibits Ca.(L) channels in a concentration-dependent manner in human mesenteric arteriolar smooth muscle cells.