Propofol inhibits muscarinic acetylcholine receptor-mediated signal transduction in Xenopus Oocytes expressing the rat M1 receptor

Atomistic Molecular Dynamics Simulations of Propofol and Fentanyl in Phosphatidylcholine Lipid Bilayers

Atomistic molecular dynamics (MD) and steered MD simulations in combination with umbrella sampling methodology were utilized to study the general anesthetic propofol and the opioid analgesic fentanyl and their interaction with lipid bilayers, which is not yet fully understood. These molecules were inserted into two different fully hydrated phospholipid bilayers, namely, dioleoylphosphatidylcholine (DOPC) and dipalmitoylphosphatidylcholine (DPPC), to investigate the effects that these drugs have on the bilayer. We determined the role of the lipid chain length and saturation on the behavior of the two drugs. Pure, fully hydrated DOPC and DPPC bilayers were also simulated, and the results were in excellent agreement with the experimental values. Various structural and mechanical properties of each system, such as the area per lipid, area compressibility modulus, order parameter, lateral lipid diffusion, hydrogen bonds, and radial distribution functions, have been calculated to assess how the drug molecules affect the different bilayers. From the calculated results, we show that fentanyl and propofol generally follow similar trends in each bilayer but adopt different favorable positions close to the headgroup/chain interface at the carbonyl groups. Propofol was shown to selectively form hydrogen bonds at the carbonyl carbon in each bilayer, whereas fentanyl interacts with water molecules at the headgroup interface. From the calculated free-energy profiles, we determined that both molecules show a preference for the low-density, low-order acyl chain region of the bilayers and both significantly preferred the DOPC bilayer with propofol and fentanyl having energy minima at -6.66 and -43.07 kcal mol^-1, respectively. This study suggests that different chain lengths and levels of saturation directly affect the properties of these two important molecules, which are seen to work together to control anesthesia in surgical applications.

Propofol inhibits carbachol-induced chloride secretion by directly targeting the basolateral K+ channel in rat ileum epithelium

BACKGROUND

Propofol is a widely used intravenous general anesthetic. Acetylcholine (ACh) is critical in controlling epithelial ion transport. This study was to investigate the effects of propofol on ACh-evoked secretion in rat ileum epithelium.

METHODS

The Ussing chamber technique was used to investigate the effects of propofol on carbachol (CCh)-evoked short-circuit currents (Isc).

KEY RESULTS

Propofol (10^-2 -10^-6  mol/L) attenuated CCh-evoked Isc of rat ileum mucosa in a dose-dependent manner. The inhibitory effect of propofol was only evident after application to the serosal side. Pretreatment with tetrodotoxin (TTX, 0.3 μmol/L, n=5) had no effect on propofol-induced inhibitory effect, whereas serosal application of K⁺ channel inhibitor, glibenclamide, but not, an ATP-sensitive K⁺ channel inhibitor, largely reduced the inhibitory effect of propofol. In addition, pretreatment with either hexamethonium bromide (HB, nicotinic nACh receptor antagonist) or Cl^- channel blockers niflumic acid and cystic fibrosis transmembrane conductance regulator (inh)-172 did not produce any effect on the propofol-induced inhibitory effect.

CONCLUSIONS & INFERENCES

Propofol inhibits CCh-induced intestinal secretion by directly targeting basolateral K⁺ channels.

The recent progress in research on effects of anesthetics and analgesics on G protein-coupled receptors

The exact mechanisms of action behind anesthetics and analgesics are still unclear. Much attention was focused on ion channels in the central nervous system as targets for anesthetics and analgesics in the 1980s. During the 1990s, major advances were made in our understanding of the physiology and pharmacology of G protein coupled receptor (GPCR) signaling. Thus, several lines of studies have shown that G protein coupled receptors (GPCRs) are one of the targets for anesthetics and analgesics and especially, that some of them inhibit the functions of GPCRs, i.e,, muscarinic receptors and substance P receptors. However, these studies had been focused on only G(q) coupled receptors. There has been little work on G(s)- and G(i)-coupled receptors. In the last decade, a new assay system, using chimera G(i/o)-coupled receptor fused to Gq(i5), has been established and the effects of anesthetics and analgesics on the function of G(i)-coupled receptors is now more easily studied. This review highlights the recent progress of the studies regarding the effects of anesthetics and analgesics on GPCRs.

Analysis of the effects of anesthetics and ethanol on mu-opioid receptor

G protein-coupled receptors, in particular, Ca(2+)-mobilizing G(q)-coupled receptors have been reported to be targets for anesthetics. Opioids are commonly used analgesics in clinical practice, but the effects of anesthetics on the opioid mu-receptors (muOR) have not been systematically examined. We report here an electrophysiological assay to analyze the effects of anesthetics and ethanol on the functions of muOR in Xenopus oocytes expressing a muOR fused to chimeric Galpha protein G(qi5) (muOR-G(qi5)). Using this system, the effects of halothane, ketamine, propofol, and ethanol on the muOR functions were analyzed. In oocytes expressing muOR-G(qi5), the( )muOR agonist DAMGO ([D-Ala(2),N-MePhe(4),Gly-ol]-enkephalin) elicited Ca(2+)-activated Cl(-) currents in a concentration-dependent manner (EC(50) = 0.24 microM). Ketamine, propofol, halothane, and ethanol themselves did not elicit any currents in oocytes expressing muOR-G(qi5), whereas ketamine and ethanol inhibited the DAMGO-induced Cl(-) currents at clinically equivalent concentrations. Propofol and halothane inhibited the DAMGO-induced currents only at higher concentrations. These findings suggest that ketamine and ethanol may inhibit muOR functions in clinical practice. We propose that the electrophysiological assay in Xenopus oocytes expressing muOR-G(qi5) would be useful for analyzing the effects of anesthetics and analgesics on opioid receptor function.

[Propofol-induced myocardial depression: possible role of atrial muscarinic cholinergic receptors]

OBJECTIVE

To investigate the possible role of muscarinic cholinergic receptors (MCRs) in the depression of myocardial function induced by propofol, an intravenous anesthetic chemically unrelated to other drugs. Although adverse effects are rare, bradycardia has been reported and this can lead to cardiac arrest in some patients. The mechanism behind this effect is still unknown but a possible role for MCRs has been suggested.

MATERIAL AND METHODS

The interaction of propofol with human atrial MCRs was determined by means of inhibition tests using [3H] quinuclidinyl benzilate ([3H] QNB).

RESULTS

The displacement of [3H] QNB binding to human atrial MCRs by propofol was concentration dependent but the observed effect was not consistent with a model of simple competition between propofol and [3H] QNB.

CONCLUSION

Propofol appears to have the ability to modify the activity of human atrial MCRs and this effect may be related to its ability to induce bradycardia.

Antimuscarinic Syndrome After Propofol Administration in the Emergency Department

Antimuscarinic syndrome (AS), a rare but serious adverse event associated with propofol should be included in the differential diagnosis of patients who develop agitation after its administration. We report a case of antimuscarinic syndrome that developed in an emergency department patient immediately after receiving propofol for the reduction of an elbow dislocation. The patient had received therapeutic doses of meperidine and promethazie several hours before the administration of propofol, and had an estimated serum ethanol level of 64 mg/dL about 1 h before sedation. The patient was successfully treated with physostigmine. Administration of propofol in conjunction with other substances known to have antimuscarinic effects may increase the risk of developing AS.

Cholinergic modulation of response properties and orientation tuning of neurons in primary visual cortex of anaesthetized Marmoset monkeys

Cortical processing is strongly influenced by the actions of neuromodulators such as acetylcholine (ACh). Early studies in anaesthetized cats argued that acetylcholine can cause a sharpening of orientation tuning functions and an improvement of the signal-to-noise ratio (SNR) of neuronal responses in primary visual cortex (V1). Recent in vitro studies have demonstrated that acetylcholine reduces the efficacy of feedback and intracortical connections via the activation of muscarinic receptors, and increases the efficacy of feed-forward connections via the activation of nicotinic receptors. If orientation tuning is mediated or enhanced by intracortical connections, high levels of acetylcholine should diminish orientation tuning. Here we investigate the effects of acetylcholine on orientation tuning and neuronal responsiveness in anaesthetized marmoset monkeys. We found that acetylcholine caused a broadening of the orientation tuning in the majority of cells, while tuning functions became sharper in only a minority of cells. Moreover, acetylcholine generally facilitated neuronal responses, but neither improved signal-to-noise ratio, nor reduced trial-to-trial firing rate variance systematically. Acetylcholine did however, reduce variability of spike occurrences within spike trains. We discuss these findings in the context of dynamic control of feed-forward and lateral/feedback connectivity by acetylcholine.

Characterization of functional effects of Z-338, a novel gastroprokinetic agent, on the muscarinic M1, M2, and M3 receptors expressed in Xenopus oocytes

This study characterized the functional effects of a novel gastroprokinetic agent, N-[2-(diisopropylamino)ethyl]-2-[(2-hydroxy-4,5-dimethoxybenzoyl)amino]-1, 3-thiazole-4-carboxyamide monohydrochloride trihydrate (Z338), on the muscarinic M1, M2, and M3 receptors expressed in Xenopus oocytes using the two-electrode voltage clamp method. Z-338 did not produce by itself any currents in oocytes expressing muscarinic M1, M3 receptors or muscarinic M2 receptors/G protein-gated inward rectifying K+ channels (Kir3.1 channels). In oocytes expressing muscarinic M1 receptors, Z-338 inhibited the acetylcholine-induced Ca2+ -activated Cl- current with an IC50 of 1.8 microM. In oocytes expressing muscarinic M2 receptors/Kir3.1 channels, Z-338 inhibited the acetylcholine-induced K+ currents with an IC50 of 10.1 microM, whereas in oocytes expressing muscarinic M3 receptors, Z-338 did not inhibit the acetylcholine-induced Ca2+ -activated Cl- current in a concentration-dependent manner. These results indicate that Z-338 is a potent antagonist not for muscarinic M3 receptor but for both muscarinic M1 and M2 receptors. Thus, Z-338 is a gastrokinetic agent with a unique profile.

Anticholinergic Syndrome After Anesthesia: A Case Report and Review

Anticholinergic syndrome may present with a wide variety of signs and symptoms. Central manifestations range from excitatory symptoms including delirium and agitation to central nervous system depression, stupor and coma. Anticholinergic syndrome was once a common phenomenon after general anesthesia because of the frequent administration of the anticholinergic agents atropine and scopolamine. Now that these agents are rarely administered, anesthesia-related anticholinergic syndrome is currently infrequently reported. Still, many prescription and over the counter medications as well as many anesthetic agents possess anticholinergic activity, and this diagnosis should be considered in patients with altered mental status following general anesthesia. We report a case of prolonged somnolence following general anesthesia for an MRI. A rapid improvement of mental status with physostigmine confirmed the diagnosis of anticholinergic syndrome. This case is unique in that anticholinergic syndrome-related respiratory depression was promptly reversed with physostigmine.

Site of action of the general anesthetic propofol in muscarinic M1 receptor-mediated signal transduction

Although a potential target site of general anesthetics is primarily the GABA A receptor, a chloride ion channel, a previous study suggested that the intravenous general anesthetic propofol attenuates the M1 muscarinic acetylcholine receptor (M1 receptor)-mediated signal transduction. In the present study, we examined the target site of propofol in M1 receptor-mediated signal transduction. Two-electrode voltage-clamp method was used in Xenopus oocytes expressing both M1 receptors and associated G protein alpha subunits (Gqalpha). Propofol inhibited M1 receptor-mediated signal transduction in a dose-dependent manner (IC50 = 50 nM). Injection of guanosine 5'-3-O-(thio)triphosphate (GTPgammaS) into oocytes overexpressing Gqalpha was used to investigate direct effects of propofol on G protein coupled with the M1 receptor. Propofol did not affect activation of Gqalpha-mediated signal transduction with the intracellular injection of GTPgammaS. We also studied effects of propofol on l-[N-methyl-3H]scopolamine methyl chloride ([3H]NMS) binding and M1 receptor-mediated signal transduction in mammalian cells expressing M1 receptor. Propofol inhibited the M1 receptor-mediated signal transduction but did not inhibit binding of [3H]NMS. Effects of propofol on Gs- and Gi/o-coupled signal transduction were investigated, using oocytes expressing the beta2 adrenoceptor (beta2 receptor)/cystic fibrosis transmembrane conductance regulator or oocytes expressing the M2 muscarinic acetylcholine receptor (M2 receptor)/Kir3.1 (a member of G protein-gated inwardly rectifying K(+) channels). Neither beta2 receptor-mediated nor M2 receptor-mediated signal transduction was inhibited by a relatively high concentration of propofol (50 microM). These results indicate that propofol inhibits M1 receptor-mediated signal transduction by selectively disrupting interaction between the receptor and associated G protein.

A functional assay for G-protein-coupled receptors using stably transformed insect tissue culture cell lines

Insect cells are an underexplored resource for functional G-protein-coupled receptor (GPCR) assays, despite a strong record in biochemical (binding) assays. Here we describe the use of vectors capable of creating stably transformed insect cell lines to generate a cell-based functional GPCR assay. This assay employs the luminescent photoprotein aequorin and the promiscuous G-protein subunit Galpha16 and is broadly applicable to human GPCRs. We demonstrate that the assay can quantitate ligand concentration-activity relationships for seven different human GPCRs, can differentiate between partial and full agonists, and can determine rank order potencies for both agonists and antagonists that match those seen with other assay systems. Human Galpha16 improves signal strength but is not required for activity with some receptors. The coexpression of human and bovine betagamma subunits and/or phospholipase Cbeta makes no difference to agonist efficacy or potency. Two different receptors expressed in the same cell line respond to their specific agonists, and two different cell lines (Sf9 and High 5) are able to functionally detect the same expressed GPCR. Sf9 cells have the capability to produce fully functional human receptors, allied to a low background of endogenous receptors, and so are a valuable system for investigating orphan GPCRs and receptor dimerization.

Propofol inhibits volume-sensitive chloride channels in human coronary artery smooth muscle cells

Volume-sensitive chloride channels (VSCC) play an important role in regulation of cell volume and electrical activity. Activation of vascular smooth muscle VSCC causes smooth muscle depolarization and contraction. We investigated the effects of propofol on VSCC in cultured human coronary artery smooth muscle cells by using the chloride-sensitive dye 6-methoxy-N-ethylquinolinium (MEQ). To activate VSCC, cells were superfused for 2 min with hypotonic gluconate solutions and then potassium thiocyanate solution. The percentage reduction in MEQ fluorescence during 60 s in the presence of potassium thiocyanate was measured and used as an index of VSCC activity. 5-Nitro-2-(3-phenylpropylamino) benzoic acid (NPPB), a well characterized chloride channel blocker, and propofol were dissolved in hypotonic gluconate solution to test their effect on VSCC activity. The reduction in fluorescence was inversely related to osmolality, indicating that activation of VSCC is osmolality dependent. Hypotonic gluconate solution (210 mOsm/kg H(2)O) reduced fluorescence by 38.9% +/- 2.6% of the baseline value. The reduction in fluorescence was dose-dependently inhibited by NPPB. Propofol at 0.3, 1, 3, 10, 30, and 100 micro g/mL significantly inhibited the reduction in fluorescence to 23.6% +/- 4.8%, 19.7% +/- 7.4%, 18.2% +/- 3.5%, 17.6% +/- 5.0%, 15.8% +/- 3.1%, and 10.3% +/- 3.9% of the baseline value, respectively. Our results indicate that propofol inhibits VSCC in a dose-dependent manner in human coronary artery smooth muscle cells.

Potentiation by propofol of the response of rat submandibular acinar cells to purinergic agonists

The effect of propofol (2,6-diisopropylphenol) on the intracellular concentration of calcium ([Ca(2+)](i)) and on the response of rat submandibular acini to purinergic agonists was studied. By itself, propofol (60 to 200 microM) slowly increased the [Ca(2+)](i) without affecting the production of inositol phosphates. The increase of the [Ca(2+)](i) involved for about 50% the mobilization of thapsigargin-sensitive intracellular calcium pools. The rest of the calcium originated from a pool distinct from mitochondria. Propofol also increased the uptake of extracellular calcium but not manganese by a mechanism inhibited by nickel. The variation of the [Ca(2+)](i) by propofol provoked a decrease of cell volume measured by light scattering. Propofol increased the effect of a maximal concentration of extracellular ATP on the [Ca(2+)](i). This interaction could be observed when propofol and ATP were added simultaneously to the medium but not when propofol had been removed from the medium before adding ATP. Among ATP analogs, propofol only increased the response to benzoyl-ATP (Bz-ATP). The blockade of P2X(7) receptors with oxidized ATP or Coomassie blue did not prevent the interaction between propofol and ATP. The effect of propofol could also be observed even when the concentration of ATP(4-) was decreased by extracellular magnesium to such a level that only P2X(4) receptors could possibly be activated by the nucleotide. Propofol had no effect on the uptake of manganese, the formation of pores and the activation of phospholipase D in response to a P2X(7) agonist. These results exclude an interaction with this receptor. It is concluded that, in rat submandibular acini, propofol can increase the [Ca(2+)](i) and decrease the cell volume. Propofol can also modulate the activation of P2X(4) receptors by extracellular nucleotides. These effects are observed at concentrations of propofol reached during the induction of anesthesia and might explain why hypersalivation has been reported as one of the side-effects of propofol.

GTP gamma S-induced Ca2+ activated Cl- currents: its stable induction by Gq alpha overexpression in Xenopus oocytes

In native Xenopus oocytes, injection of guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) (30 mM, 5 nl) did not induce Cl- current in 11 out of 22 oocytes. Injection of increased concentration of GTPgammaS (100 mM, 5 nl) into the oocytes induced Cl- currents in 16 out of 17 oocytes; however, the size of the induced currents was extremely varied. In oocytes overexpressing Gq alpha, GTPgammaS (30 mM, 5 nl) faithfully evoked Ca2+-activated Cl- currents. These results indicate that heterogeneous expression of Gq alpha in Xenopus oocytes provides a useful system for studying the functional roles of Gq alpha in regulating cellular events.