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Biomedical subjects

Munehiro Shiraishi

Publications and source records attributed to Munehiro Shiraishi.

At least 19 recordsLinked to original sources
PubMed2006

The tramadol metabolite, O-desmethyl tramadol, inhibits 5-hydroxytryptamine type 2C receptors expressed in Xenopus Oocytes.

PURPOSE: Tramadol is widely used clinically as an analgesic, yet the mechanism by which it produces antinociception remains unclear. O-Desmethyl tramadol, the main metabolite of tramadol, is a more potent analgesic than tramadol. We reported previously that tramadol inhibits the 5-hydroxytryptamine (5-HT) type 2C receptor (5-HT(2C)R), a G-protein-coupled receptor that is expressed widely within brain and that mediates several effects of 5-HT, including nociception, feeding, and locomotion. The effects of O-desmethyl tramadol on 5-HT(2C)R have not been studied. In this study, we investigated the effect of O-desmethyl tramadol on 5-HT(2C)R expressed in Xenopus oocytes. METHODS: We examined the effect of O-desmethyl tramadol on 5-HT(2C)R using the Xenopus oocyte expression system. Furthermore, we investigated the effects of O-desmethyl tramadol on the binding of [(3)H]5-HT by 5-HT(2C)R. RESULTS: O-Desmethyl tramadol, at pharmacologically relevant concentrations, inhibited 5-HT-evoked Ca(2+)-activated Cl(-) currents in oocytes that expressed 5-HT(2C)R. The inhibitory effect of O-desmethyl tramadol on 5-HT(2C)R was overcome at higher concentrations of 5-HT. Bisindolylmaleimide I (GF109203X), a protein kinase C inhibitor, increased 5-HT-evoked currents but had little effect on the inhibition of 5-HT-evoked currents by O-desmethyl tramadol. O-Desmethyl tramadol inhibited the specific binding of [(3)H]5-HT by 5-HT(2C)R expressed in oocytes. O-Desmethyl tramadol altered the apparent dissociation constant for binding of [(3)H]5-HT by 5-HT(2C)R without changing maximum binding, which indicated competitive inhibition. CONCLUSION: These results suggest that O-desmethyl tramadol inhibits 5-HT(2C)R, which provides further insight into the pharmacological properties of tramadol and O-desmethyl tramadol.

Animals↗
PubMed2006

Effects of anesthetics on mutant N-methyl-D-aspartate receptors expressed in Xenopus oocytes.

Alcohols, inhaled anesthetics, and some injectable anesthetics inhibit the function of N-methyl-d-aspartate (NMDA) receptors, but the mechanisms responsible for this inhibition are not fully understood. Recently, it was shown that ethanol inhibition of NMDA receptors was reduced by mutation of residues in the transmembrane (TM) segment 3 of the NR1 subunit (F639A) or in TM4 of the NR2A subunit (A825W), suggesting putative ethanol binding sites. We hypothesized that the actions of other anesthetics might also require these amino acids and evaluated the effects of anesthetics on the NMDA receptors expressed in Xenopus oocytes with two-electrode voltage-clamp recording. Effects of hexanol, octanol, isoflurane, halothane, chloroform, cyclopropane, 1-chloro-1,2,2-trifluorocyclobutane, and xenon were reduced or eliminated in the mutant NMDA receptors, whereas the inhibitory effects of nitrous oxide, ketamine, and benzene were not affected by these mutations. Rapid applications of glutamate and glycine by a T-tube device provided activation time constants, which suggested different properties of ketamine and isoflurane inhibition. Thus, amino acids in TM3 and TM4 are important for the actions of many anesthetics, but nitrous oxide, benzene, and ketamine seem to have distinct mechanisms for inhibition of the NMDA receptors.

Amino Acid Substitution↗
PubMed2005

The effects of the neurosteroids: pregnenolone, progesterone and dehydroepiandrosterone on muscarinic receptor-induced responses in Xenopus oocytes expressing M1 and M3 receptors.

The neurosteroids pregnenolone, progesterone, and dehydroepiandrosterone (DHEA) occur naturally in the nervous system. They act on neural tissues, participate in neuronal signaling, and are reported to alter neuronal excitability via nongenomic mechanisms. Muscarinic receptors have important roles in neuronal functions in the brain and autonomic nervous system. In this study, we investigated the effects of pregnenolone, progesterone, and DHEA on M(1) and M(3) muscarinic receptors using the Xenopus oocyte expression system. Pregnenolone and progesterone inhibited the acetylcholine (ACh)-mediated responses of M(1) and M(3) receptors expressed in Xenopus oocytes, whereas DHEA did not. The half-maximal inhibitory concentrations (IC(50)) for pregnenolone inhibition of M(1) receptor- and M(3) receptor-mediated currents were 11.4 and 6.0 microM respectively; the IC(50) values for progesterone inhibition of M(1) receptor- and M(3) receptor-mediated currents were 2.5 and 3.0 microM respectively. The selective protein kinase C (PKC) inhibitor GF109203X had little effect on the pregnenolone or progesterone inhibition of the ACh-induced currents in Xenopus oocytes expressing M(1) or M(3) receptors. The inhibitory effects of pregnenolone and progesterone were overcome at higher concentrations of ACh. Pregnenolone and progesterone inhibited the [(3)H]quinuclidinyl benzilate (QNB) binding to M(1) and M(3) receptor expressed in Xenopus oocytes, and Scatchard plot analysis of [(3)H]QNB binding revealed that pregnenolone and progesterone altered the K(d) value and the B(max), indicating noncompetitive inhibition. In conclusion, pregnenolone and progesterone inhibited M(1) and M(3) receptor functions noncompetitively by the mechanism independent of PKC and by interfering with ACh binding to the receptors.

Acetylcholine↗
PubMed2005

The effects of the tramadol metabolite O-desmethyl tramadol on muscarinic receptor-induced responses in Xenopus oocytes expressing cloned M1 or M3 receptors.

O-desmethyl tramadol is one of the main metabolites of tramadol. It has been widely used clinically and has analgesic activity. Muscarinic receptors are involved in neuronal functions in the brain and autonomic nervous system, and much attention has been paid to these receptors as targets for analgesic drugs in the central nervous system. We have reported that tramadol inhibits the function of type-1 muscarinic (M(1)) receptors and type-3 muscarinic (M(3)) receptors, suggesting that muscarinic receptors are sites of action of tramadol. However, the effects of O-desmethyl tramadol on muscarinic receptor functions have not been studied in detail. In this study, we investigated the effects of O-desmethyl tramadol on M(1) and M(3) receptors, using the Xenopus oocyte expression system. O-desmethyl tramadol (0.1-100 microM) inhibited acetylcholine (ACh)-induced currents in oocytes expressing the M(1) receptors (half-maximal inhibitory concentration [IC(50)] = 2 +/- 0.6 microM), whereas it did not suppress ACh-induced currents in oocytes expressing the M(3) receptor. Although GF109203X, a protein kinase C inhibitor, increased the ACh-induced current, it had little effect on the inhibition of ACh-induced currents by O-desmethyl tramadol in oocytes expressing M(1) receptors. The inhibitory effect of O-desmethyl tramadol on M(1) receptor was overcome when the concentration of ACh was increased (K(D) with O-desmethyl tramadol = 0.3 microM). O-desmethyl tramadol inhibited the specific binding of [(3)H]quinuclidinyl benzilate ([(3)H]QNB) to the oocytes expressed M(1) receptors (IC(50) = 10.1 +/- 0.1 microM), whereas it did not suppress the specific binding of [(3)H]QNB to the oocytes expressed M(3) receptors. Based on these results, O-desmethyl tramadol inhibits functions of M(1) receptors but has little effect on those of M(3) receptors. This study demonstrates the molecular action of O-desmethyl tramadol on the receptors and may help to explain its neural function.

Acetylcholine↗
PubMed2005

Gargling with sodium azulene sulfonate reduces the postoperative sore throat after intubation of the trachea.

Postoperative sore throat (POST) is a complication that remains to be resolved in patients undergoing endotracheal intubation. In this study, we investigated whether preoperative gargling with sodium 1,4-dimethyl-7-isopropylazulene-3-sulfonate monohydrate (sodium azulene sulfonate, Azunol) reduces POST after endotracheal intubation. Forty patients scheduled for elective surgery under general anesthesia were randomized into Azunol and control groups. In the Azunol group, patients gargled with 4 mg Azunol diluted with 100 mL tap water (40 microg/mL). In the control group, patients gargled with 100 mL of tap water. After emergence from general anesthesia, the patients with POST were counted and POST was evaluated using a verbal analog pain scale. There were no significant differences between the two groups by age, height, body weight, gender distribution, or duration of anesthesia and surgery. In the control group, 13 patients (65%) complained of POST, which remained 24 h later in nine patients (45%). In the Azunol group, five patients (25%) also complained of POST, which completely disappeared by 24 h later. The incidence of POST and verbal analog pain scale scores in the Azunol group decreased significantly compared with the control group. We demonstrated that gargling with Azunol effectively attenuated POST with no adverse reactions.

Administration, Oral↗
PubMed2005

[Complications related to anesthesia method in the University of Occupational and Environmental Health Hospital].

BACKGROUND: Complications related to anesthesia remain a problem. We studied the incidence of complications during anesthesia in 2758 patients who had undergone anesthesia in the University of Occupational and Environmental Health Hospital. METHODS: We checked the anesthesia records retrospectively and analyzed the collected data for the incidence of complications during anesthesia. RESULTS: The total incidence of complications during anesthesia was 12.2%. The incidences of complication are estimated to be 13.4% in inhalation anesthesia, 11.9% in inhalation anesthesia plus epidural, spinal or conduction block, 8.9% in CSEA, zero % in epidural anesthesia and 7.5% in spinal anesthesia. CONCLUSIONS: The incidence of complications in inhalation anesthesia was almost as same as that in inhalation anesthesia plus epidural, spinal or conduction block. More study should be necessary to prevent complications related to anesthesia.

Anesthesia↗
PubMed2005

[Anesthetic management of a patient in whom one-lung ventilation occurred due to an incorrectly positioned stent].

Stents are inserted for severe stenosis of the trachea owing to malignant tumors, but an incorrectly positioned stent can cause airway obstruction. Here, we report the anesthetic management of a patient undergoing removal of an incorrectly positioned stent. A 56-year-old man had a stent inserted in the trachea for stenosis caused by a tumor. One month later, he was scheduled for reinsertion of a stent for tracheal stenosis owing to growth of the tumor, but the stent was inserted in the left main bronchus interfering ventilation to the right lung. Therefore, removal of the stent under general anesthesia was scheduled. As the stent was to be removed from an incision in the cricoid, we had to maintain deep anesthesia to maintain immobility, keeping spontaneous respiration in case we could not ventilate during surgery. Since inhaled anesthetics are insufficient to maintain deep anesthesia, we anesthetized the patient with an intravenous anesthetic, sevoflurane and continuous propofol infusion. Propofol allows spontaneous respiration better than opioids. With this method we were able to anesthetize the patient maintaining spontaneous respiration and oxygenation with stable vital signs during surgery.

Anesthesia, General↗
PubMed2004

Effects of alcohols and anesthetics on recombinant voltage-gated Na+ channels.

Voltage-gated Na(+) channels (Na(+) channels) mediate the rising phase of action potentials in neurons and excitable cells. Nine subtypes of the alpha subunit (Na(v)1.1-Na(v)1.9) have been shown to form functional Na(+) channels to date. Recently, anesthetic concentrations of volatile anesthetics and ethanol were reported to inhibit Na(+) channel functions, but it is not known whether all subtypes are inhibited by anesthetics. To investigate possible subtype-specific effects of anesthetics on Na(+) channels, mRNA of Na(v)1.2, Na(v)1.4, Na(v)1.6, and Na(v)1.8 alpha subunit-encoded genes were injected individually or together with a beta subunit mRNA into Xenopus oocytes. Na(+) currents were recorded using the two-electrode voltage-clamp technique. Isoflurane, at clinically relevant concentrations, inhibited the currents produced by Na(v)1.2, Na(v)1.4, and Na(v)1.6 by approximately 10% at the holding potential of -90 mV and by approximately 30% at -60 mV, but it did not affect the Na(v)1.8-mediated current. An anesthetic fluorocyclobutane (1-chloro-1,2,2-trifluorocyclobutane) also inhibited the Na(v)1.2 channel, whereas the nonanesthetic fluorocyclobutane (1,2-dichlorohexafluorocyclobutane) had no effect. The perfluorinated heptanol [CF(3)(CF(2))(5)CH(2)OH], which produces anesthesia, inhibited the Na(v)1.2 channel like other alcohols tested (ethanol, heptanol, and CF(3)CH(2)OH), even though this compound does not affect GABA, glycine, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid, or kainate receptors. In contrast, most intravenous anesthetics did not have significant effects on the Na(v)1.2 channel at clinically relevant concentrations although urethane inhibited. These results show that isoflurane inhibits the Na(+) channel functions except Na(v)1.8 in a voltage-dependent manner. These findings indicate that the Na(+) channel is a neuronal target for anesthetic action.

Alcohols↗
PubMed2004

A forskolin derivative, colforsin daropate hydrochloride, inhibits the decrease in cortical renal blood flow induced by noradrenaline or angiotensin II in anesthetized rats.

A forskolin derivative, colforsin daropate hydrochloride (CDH), acts directly on adenylate cyclase to increase the intracellular cyclic adenosine monophosphate levels which produce a positive inotropic effect and a lower blood pressure. However, little is known about the effects of CDH on the renal function. We used laser Doppler flowmetry to measure the cortical renal blood flow (RBF) in male Wistar rats given a continuous intravenous infusion of CDH and evaluated the effects of CDH on the noradrenaline (NA) and angiotensin II (AngII) induced increases in blood pressure and reductions in RBF. Continuous intravenous administration of CDH at 0.25 microg/kg/min did not affect the mean arterial pressure (MAP), but increased heart rate and RBF. Continuous intravenous administration of CDH at high doses (0.5-0.75 microg/kg/min) decreased the MAP, with little effect on the RBF. The administration of exogenous NA (1.7 microg/kg) increased the MAP and decreased the RBF. However, a bolus injection of NA did not decrease the RBF during continuous intravenous administration of CDH, and CDH did not affect the NA-induced increase in MAP. The administration of exogenous AngII (100 ng/kg) increased MAP and decreased RBF and heart rate, but a bolus injection of AngII did not decrease RBF during continuous intravenous administration of CDH. These results suggest that CDH plays a protective role against the pressor effects and the decrease in RBF induced by NA or AngII.

Anesthesia↗
PubMed2004

Analysis of the effects of halothane on Gi-coupled muscarinic M2 receptor signaling in Xenopus oocytes using a chimeric G alpha protein.

Metabotropic G protein-coupled receptors have recently been recognized as targets for anesthetics and analgesics. In particular, G(q)-coupled receptors such as muscarinic M(1) receptors (M(1)R) and 5-hydroxytryptamine (5-HT) type 2A receptors have been reported to be targets for anesthetics. Much less is known, however, about the effects of anesthetics on G(i)-coupled receptors. Here we report a method to analyze functions of G(i)-coupled receptors in Xenopus oocytes expressing a chimeric G alpha protein. A chimeric G alpha(q) protein G alpha(qi5), which contains carboxy-terminus five amino acids of G alpha(i), enables G(i)-coupled receptors to couple to Gq-coupled receptor-mediated downstream pathways such as activation of phospholipase C. We determined acetylcholine (ACh)-induced Ca(2+)-activated Cl(-) currents in Xenopus oocytes coexpressing G(i)-coupled muscarinic M(2)receptors (M(2)R) with the chimeric G alpha(qi5). Although ACh did not induce any currents in oocytes expressing M(2)R alone, it caused robust Cl(-) currents in oocytes coexpressing M(2)R with G alpha(qi5). The EC(50) of the ACh-induced Cl(-) current mediated through G alpha(qi5) was 0.2 micromol/l, which was 2.2 times higher than that of the ACh-induced G protein-activated inwardly rectifying K(+) currents activated by G beta gamma subunits liberated from endogenously expressed G alpha(i) in Xenopus oocytes. Other G(i)-coupled somatostatin type 2, 5-HT(1A) and delta-opioid receptors, when coexpressed with G alpha(qi5) in oocytes, also caused robust Ca(2+)-activated Cl(-) currents. In oocytes coexpressing M(2)R and G alpha(qi5), a volatile anesthetic halothane inhibited M(2)R-induced Cl(-) currents in a concentration-dependent manner with the IC(50) of 1.1 mmol/l, suggesting that halothane inhibits M(2)R-induced cellular responses at clinically relevant concentrations. Treatment with the protein kinase C inhibitor GF109203X produced a 3.5-fold enhancement of the initial Cl(-) currents induced by 1 micromol/l ACh in oocytes expressing M(2)R and G(qi5). The rate of halothane-induced inhibition of Cl(-) currents elicited by ACh, however, was not changed in such oocytes pretreated with GF109203X. These findings suggest that halothane inhibits the M(2)R-induced signaling by acting at sites other than PKC activity. Collectively these findings suggest that the use of oocyte expressing G alpha(qi5) would be helpful to examine the effects of anesthetics or analgesics on the function of G(i)-coupled receptors in the Xenopus oocyte expression system.

Acetylcholine↗
PubMed2004

The inhibitory effects of tramadol on 5-hydroxytryptamine type 2C receptors expressed in Xenopus oocytes.

UNLABELLED: Although tramadol is widely available as an analgesic, its mechanism of antinociception remains unresolved. Serotonin (5-hydroxytryptamine, 5-HT) is a monoaminergic neurotransmitter that modulates numerous sensory, motor, and behavioral processes. The 5-HT type 2C receptor (5-HT(2C)R) is one of the major 5-HT receptor subtypes and is implicated in many important effects of 5-HT, including pain, feeding, and locomotion. In this study, we used a whole-cell voltage clamp to examine the effects of tramadol on 5-HT-induced Ca(2+)-activated Cl(-) currents mediated by 5-HT(2C)R expressed in Xenopus oocytes. Tramadol inhibited 5-HT-induced Cl(-) currents at pharmacologically relevant concentrations. The protein kinase C (PKC) inhibitor, bisindolylmaleimide I (GF109203x), did not abolish the inhibitory effects of tramadol on the 5-HT(2C)R-mediated events. We also studied the effects of tramadol on [(3)H]5-HT binding to 5-HT(2C)R expressed in Xenopus oocytes, and found that it inhibited the specific binding of [(3)H]5-HT to 5-HT(2C)R. Scatchard analysis of [(3)H]5-HT binding revealed that tramadol altered the apparent dissociation constant for binding without changing maximal binding, indicating competitive inhibition. The results suggest that tramadol inhibits 5-HT(2C)R function, and the mechanism of this inhibitory effect seems to involve competitive displacement of the 5-HT binding to the 5-HT(2C)R, rather than via activation of the PKC pathway. IMPLICATIONS: We examined the effects of tramadol on 5-hydroxytryptamine type 2C receptor (5-HT(2C)R) expressed in Xenopus oocytes. Tramadol inhibited 5-HT(2C)R function and the specific binding of [(3)H]5-HT to 5-HT(2C)R in a competitive manner. From these data, the mechanism of the inhibitory effect on 5-HT(2C)R might involve the competitive displacement of 5-HT binding to the 5-HT(2C)R.

Analgesics, Opioid↗
PubMed2004

The inhibition of aortic smooth muscle cell proliferation by the intravenous anesthetic ketamine.

Smooth muscle cell (SMC) proliferation has been recognized as central to the pathology of both major forms of vascular disease, atherosclerosis and hypertension. Recently, we reported that ketamine inhibits rat mesangial cell proliferation, suggesting that ketamine inhibits cell growth. Although the IV anesthetic ketamine has been widely used clinically, the exact effects of ketamine on vascular SMC proliferation have not been studied. In this study, we investigated the effects of ketamine on vascular SMC proliferation. Ketamine inhibited [(3)H]thymidine incorporation and decreased the number of SMCs in a concentration-dependent manner (10-200 microM); neither propofol nor fentanyl inhibited [(3)H]thymidine incorporation into human aortic SMCs. The protein kinase C (PKC) inhibitor GF109203x abolished the ketamine-induced inhibition of [(3)H]thymidine incorporation into SMC, but the inhibition was not affected by either the protein kinase A inhibitor H-89 or the protein kinase G inhibitor KT5823. A histological analysis demonstrated the inhibitory effect of ketamine on the intimal thickening of the balloon-injured rat aorta. Based on these results, ketamine inhibits SMCs at clinical concentrations via the PKC pathway. Our results indicate that ketamine might prevent the proliferation of SMCs clinically.

Anesthetics, Dissociative↗
PubMed2003

Effects of the intravenously administered anaesthetics ketamine, propofol, and thiamylal on the cortical renal blood flow in rats.

Intravenous anaesthetics such as ketamine, propofol, and thiamylal are widely used, although the direct effects of these anaesthetics on the renal blood flow (RBF) have not been well elucidated. In this study, we examined the effects of bolus and continuous administrations of ketamine, propofol, and thiamylal on cortical RBF and the effects of noradrenaline (NA) on RBF under continuous administration of these anaesthetics. We used laser Doppler flowmetry to measure the effects of bolus injection and continuous infusion of ketamine, propofol, and thiamylal on cortical RBF in male Wistar rats. We also examined the effects of the anaesthetics on mean arterial blood pressure (MAP) and heart rate (HR). Bolus injections of ketamine, propofol, or thiamylal (1-8 mg/kg each, n = 10) at clinically relevant concentrations did not affect MAP, HR, or RBF. Continuous administration of ketamine, propofol, or thiamylal (1-8 mg/kg/h each, n = 10) did not affect MAP, HR or RBF. Exogenous NA (2 microg/kg) caused an increase in MAP and a decrease in RBF and HR. In experiments with continuous infusions of propofol or thiamylal (1-8 mg/kg/h each, n = 10), similar results were observed without infusion of any anaesthetics. However, bolus injection of NA did not result in a decrease in RBF during continuous ketamine infusion (98.8 +/- 6.7% of control, n = 6, p < 0.05), while ketamine did not affect the NA-induced increase in MAP. In conclusion, bolus and continuous administrations of ketamine, propofol, and thiamylal did not affect the RBF. From our present findings, ketamine would be useful for maintaining the RBF.

Anesthetics, Intravenous↗
PubMed2003

The inhibitory effects of ketamine and pentobarbital on substance p receptors expressed in Xenopus oocytes.

UNLABELLED: Substance P receptors (SPR) modulate nociceptive transmission within the spinal cord. The effects of IV anesthetics on SPR are not clear. In this study, we investigated the effects of IV anesthetics on SPR expressed in Xenopus oocytes. We examined the effects of ketamine, pentobarbital, propofol, and tramadol on SP-induced Ca(2+)-activated Cl(-) currents mediated by SPR expressed in Xenopus oocytes using a whole-cell voltage clamp. Ketamine and pentobarbital inhibited the SPR-induced currents at pharmacologically relevant concentrations, but propofol and tramadol had little effect on the currents. We also studied the effects of ketamine and pentobarbital on [(3)H]-SP to SPR. Ketamine and pentobarbital inhibited the specific binding of [(3)H]-SP to SPR expressed in Xenopus oocytes. Scatchard analysis of [(3)H]-SP binding revealed that ketamine and pentobarbital decreased the apparent dissociation constant for binding and maximal binding, indicating noncompetitive inhibition. The protein kinase C (PKC) inhibitor bisindolylmaleimide I did not abolish the inhibitory effects of ketamine and pentobarbital on SP-induced Ca(2+)-activated Cl(-) currents. The results suggest that ketamine and pentobarbital inhibit SPR function. The mechanism of their inhibition on SPR function could not be through activation of the PKC pathway and may be due to noncompetitive displacing the SP binding. IMPLICATIONS: We investigated the effects of IV anesthetics on substance P receptors (SPR) expressed in Xenopus oocytes. Ketamine and pentobarbital inhibit SPR function via noncompetitive displacing SP binding. The findings imply that the inhibition of SPR function by these compounds may play a role in the analgesic effects of these IV anesthetics.

Aluminum Compounds↗
PubMed2003

The inhibitory effects of alphaxalone on M1 and M3 muscarinic receptors expressed in Xenopus oocytes.

UNLABELLED: Alphaxalone is a neurosteroid anesthetic, but its mechanisms of action are not completely understood. Muscarinic receptors are involved in a variety of neuronal functions in the brain and autonomic nervous system, and much attention has been paid to them as targets of anesthetics. In this study, we investigated the effects of alphaxalone on M(1) and M(3) muscarinic receptors using the Xenopus oocyte expression system. Alphaxalone inhibited acetylcholine-induced currents in oocytes expressing M(1) receptors at clinically relevant concentrations. Alphaxalone also suppressed acetylcholine-induced currents in oocytes expressing M(3) receptors. The half-maximal inhibitory concentration values for the inhibition of M(1)- and M(3)-mediated currents were 1.8 +/- 0.6 micro M and 5.3 +/- 1.0 micro M, respectively. GF109203X, a selective protein kinase C inhibitor, had little effect on the inhibition of acetylcholine-induced currents by alphaxalone in oocytes expressing these receptors. Alphaxalone inhibited the specific binding of [(3)H]quinuclidinyl benzilate to oocytes expressing M(1) or M(3) receptors. These findings suggest that alphaxalone at clinically relevant concentrations inhibits the function of M(1) and M(3) receptors through a protein kinase C-independent mechanism by interfering with the [(3)H]quinuclidinyl benzilate binding sites on the receptors. IMPLICATIONS: Alphaxalone, a neurosteroid anesthetic, inhibited the function of muscarinic M(1) and M(3) receptors and the specific binding of [(3)H]quinuclidinyl benzilate ([(3)H]QNB) to oocytes expressing these receptors. These findings suggest that alphaxalone inhibits these receptors by interfering with the QNB binding sites.

Acetylcholine↗
PubMed2002

Inhibitory effects of tramadol on nicotinic acetylcholine receptors in adrenal chromaffin cells and in Xenopus oocytes expressing alpha 7 receptors.

1. Tramadol has been used clinically as an analgesic; however, the mechanism of its analgesic effects is still unknown. 2. We used bovine adrenal chromaffin cells to investigate effects of tramadol on catecholamine secretion, nicotine-induced cytosolic Ca(2+) concentration ([Ca(2+)](i)) increases and membrane current changes. We also investigated effects of tramadol on alpha7 nicotinic acetylcholine receptors (AChRs) expressed in Xenopus oocytes. 3. Tramadol concentration-dependently suppressed carbachol-induced catecholamine secretion to 60% and 27% of the control at the concentration of 10 and 100 microM, respectively, whereas it had little effect on veratridine- or high K(+)-induced catecholamine secretion. 4. Tramadol also suppressed nicotine-induced ([Ca(2+)](i)) increases in a concentration-dependent manner. Tramadol inhibited nicotine-induced inward currents, and the inhibition was unaffected by the opioid receptor antagonist naloxone. 5. Tramadol inhibited nicotinic currents carried by alpha7 receptors expressed in Xenopus oocytes. 6. Tramadol inhibited both alpha-bungarotoxin-sensitive and -insensitive nicotinic currents in bovine adrenal chromaffin cells. 7. In conclusion, tramadol inhibits catecholamine secretion partly by inhibiting nicotinic AChR functions in a naloxone-insensitive manner and alpha7 receptors are one of those inhibited by tramadol.

Adrenal Medulla↗
PubMed2002

The inhibitory effects of anesthetics and ethanol on substance P receptors expressed in Xenopus oocytes.

UNLABELLED: The neuropeptide substance P (SP) modulates nociceptive transmission within the spinal cord. SP is unique to a subpopulation of C fibers found within primary afferent nerves. However, the effects of anesthetics on the SP receptor (SPR) are not clear. In this study, we investigated the effects of volatile anesthetics and ethanol on SPR expressed in Xenopus oocytes. We examined the effects of halothane, isoflurane, enflurane, diethyl ether, and ethanol on SP-induced currents mediated by SPR expressed in Xenopus oocytes, by using a whole-cell voltage clamp. All the volatile anesthetics tested, and ethanol, inhibited SPR-induced Ca(2+)-activated Cl(-) currents at pharmacologically relevant concentrations. The protein kinase C inhibitor bisindolylmaleimide I (bisindolylmaleimide) enhanced the SP-induced Cl(-) currents. However, bisindolylmaleimide abolished the inhibitory effects on SPR of the volatile anesthetics examined and of ethanol. These results demonstrate that halothane, isoflurane, enflurane, diethyl ether, and ethanol inhibit the function of SPR and suggest that activation of protein kinase C is involved in the mechanism of action of anesthetics and ethanol on the inhibitory effects of SPR. IMPLICATIONS: We examined the effects of halothane, isoflurane, enflurane, diethyl ether, and ethanol on substance P receptor (SPR) expressed in Xenopus oocytes, by using a whole-cell voltage clamp. All the anesthetics and ethanol inhibited SPR function, and the protein kinase C (PKC) inhibitor abolished these inhibitions. These results suggest that anesthetics and ethanol inhibit SPR function via PKC.

Anesthetics, Inhalation↗