Effects of propofol on recombinant AMPA receptor channels

Intravenous Anesthetic, Propofol Affects Synaptic Responses in Cerebellar Purkinje Cells

Objective

Propofol is an intravenously administered anesthetic that enhances γ-aminobutyric acid-mediated inhibition in the central nerve system. Other mechanisms may also be involved in general anesthesia. Propofol has been implicated in movement disorders. The cerebellum is important for motor coordination and motor learning. The aim of the present study was to investigate the propofol effect on excitatory synaptic transmissions in cerebellar cortex.

Methods

Excitatory postsynaptic currents by parallel fiber stimulation and complex spikes by climbing fiber stimulation were monitored in Purkinje cells of Wister rat cerebellar slice using whole-cell patch-clamp techniques.

Results

Decay time, rise time and amplitude of excitatory postsynaptic currents at parallel fiber Purkinje cell synapses and area of complex spikes at climbing fiber Purkinje cell synapses were significantly increased by propofol administration.

Conclusion

The detected changes of glutamatergic synaptic transmission in cerebellar Purkinje cell, which determine cerebellar motor output, could explain cerebellar mechanism of motor deficits induced by propofol.

Propofol selectively alters GluA1 AMPA receptor phosphorylation in the hippocampus but not prefrontal cortex in young and aged mice

Propofol is a commonly used general anesthetic agent which has been previously shown to enhance the inhibitory GABAergic transmission in the central nervous system. In addition to the GABAergic element, the excitatory transmission may be another central molecular site impacted by propofol. Increasing evidence implies that the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor represents an excitatory amino acid receptor subtype subjected to the regulation by propofol. Indeed, in this study, we found that a single injection of propofol at an anesthetic dose increased AMPA receptor GluA1 subunit phosphorylation in young (2-3 months old) and aged (20-21 months old) mice in vivo. Propofol caused an increase in GluA1 phosphorylation in the hippocampus but not in the prefrontal cortex. The propofol effect was also site-selective as the drug elevated GluA1 phosphorylation at serine 831 (S831) but not serine 845. Interestingly, while propofol induced a moderate and transient increase in S831 phosphorylation in young mice, the drug caused a substantial and sustained S831 phosphorylation in aged animals. Total GluA1 abundance remained stable in the hippocampus and prefrontal cortex in both young and aged mice in response to propofol. These results provide evidence supporting the sensitivity of GluA1 AMPA receptors to propofol. A single dose of propofol was able to upregulate GluA1 phosphorylation in the confined hippocampus in an age-dependent manner.

Dynamic loss of surface-expressed AMPA receptors in mouse cortical and striatal neurons during anesthesia

Ionotropic glutamate receptors, especially the α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor subtype, undergo dynamic trafficking between the surface membrane and intracellular organelles. This trafficking activity determines the efficacy and strength of excitatory synapses and is subject to modulation by changing synaptic inputs. Given the possibility that glutamate receptors in the central nervous system might be a sensitive target of anesthetic agents, this study investigated the possible impact of anesthesia on trafficking and subcellular expression of AMPA receptors in adult mouse brain neurons in vivo. We found that anesthesia induced by a systemic injection of pentobarbital did not alter total protein levels of three AMPA receptor subunits (GluR1-3) in cortical neurons. However, an anesthetic dose of pentobarbital reduced GluR1 and GluR3 proteins in the surface pool and elevated these proteins in the intracellular pool of cortical neurons. The similar redistribution of GluR1/3 was observed in mouse striatal neurons. Pentobarbital did not significantly alter GluR2 expression in the two pools. Chloral hydrate at an anesthetic dose also reduced surface GluR1/3 expression and increased intracellular levels of these proteins. The effect of pentobarbital on subcellular distribution of AMPA receptors was reversible. Altered subcellular distribution of GluR1/3 returned to normal levels after the anesthesia subsided. These data indicate that anesthesia induced by pentobarbital and chloral hydrate can alter AMPA receptor trafficking in both cortical and striatal neurons. This alteration is characterized by the concurrent loss and addition of GluR1/3 subunits in the respective surface and intracellular pools.

Potentiating action of propofol at GABAA receptors of retinal bipolar cells

PURPOSE

Propofol (2,6-diisopropyl phenol), a widely used systemic anesthetic, is known to potentiate GABA(A) receptor activity in a number of CNS neurons and to produce changes in electroretinographically recorded responses of the retina. However, little is known about propofol's effects on specific retinal neurons. The authors investigated the action of propofol on GABA-elicited membrane current responses of retinal bipolar cells, which have both GABA(A) and GABA(C) receptors.

METHODS

Single, enzymatically dissociated bipolar cells obtained from rat retina were treated with propofol delivered by brief application in combination with GABA or other pharmacologic agents or as a component of the superfusing medium.

RESULTS

When applied with GABA at subsaturating concentrations and with TPMPA (a known GABA(C) antagonist), propofol markedly increased the peak amplitude and altered the kinetics of the response. Propofol increased the response elicited by THIP (a GABA(A)-selective agonist), and the response was reduced by bicuculline (a GABA(A) antagonist). The response to 5-methyl I4AA, a GABA(C)-selective agonist, was not enhanced by propofol. Serial brief applications of (GABA + TPMPA + propofol) led to a progressive increase in peak response amplitude and, at higher propofol concentrations, additional changes that included a prolonged time course of response recovery. Pre-exposure of the cell to perfusing propofol typically enhanced the rate of development of potentiation produced by (GABA + TPMPA + propofol) applications.

CONCLUSIONS

Propofol exerts a marked and selective potentiation on GABA(A) receptors of retinal bipolar cells. The data encourage the use of propofol in future studies of bipolar cell function.

Synaptic currents and transmitter responses in human NT2 neurons differentiated in aggregate culture

Postmitotic neurons were generated from the human NT2 teratocarcinoma cell line in a novel cell aggregate differentiation procedure. The NT2 model neurons express punctate immunoreactivity for synapsin and for cell markers related to GABAergic and glutamatergic neurotransmission. Using the outside-out patch-clamp configuration, we characterized the kinetics of currents elicited by a rapid application of the amino acid neurotransmitters. Moreover, we detected spontaneous postsynaptic currents in glia free cell cultures that may result from the firing activity of glutamatergic and GABAergic NT2 neurons. These cultured spontaneously active networks may be a useful tool to analyze factors that modulate the formation and efficacy of synapses between human neurons.

Modulation of AMPA receptor GluR1 subunit phosphorylation in neurons by the intravenous anaesthetic propofol

BACKGROUND

The ionotropic glutamate receptor is a potential molecular site in the central nervous system that general anaesthetics may interact with to produce some of their biological actions. Protein phosphorylation has been well documented to occur in the intracellular C-terminal domain of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) subtype of glutamate receptors, which represents a pivotal mechanism for the post-translational modulation of AMPA receptor functions. In this study, we investigated a possible influence of an i.v. anaesthetic agent propofol on the phosphorylation of AMPA receptor GluR1 subunits in cultured neurons.

METHODS

The effect of propofol on phosphorylation of GluR1 subunits at serine 831 and 845 was assayed in cultured rat striatal and cortical neurons by western blot with phospho- and site-specific antibodies.

RESULTS

Propofol consistently elevated phosphorylation of GluR1 subunits at the C-terminal serine 845 site in both striatal and cortical neurons. The elevation in phosphorylation was concentration-dependent and started at a low concentration (3 microM). This increase in serine 845 phosphorylation was rapid and sustained during the entire course of propofol exposure. In contrast to serine 845, phosphorylation of GluR1 at serine 831 was not altered by propofol in striatal and cortical neurons. Total GluR1 abundance remained unchanged in response to propofol incubation.

CONCLUSIONS

These data indicate that propofol possesses the ability to upregulate AMPA receptor GluR1 subunit phosphorylation at a specific serine 845 site in neurons and provide evidence supporting the AMPA receptor as a molecular target for general anaesthetics.