Convergent analysis of cDNA and short oligomer microarrays, mouse null mutants and bioinformatics resources to study complex traits

Gene expression data sets have recently been exploited to study genetic factors that modulate complex traits. However, it has been challenging to establish a direct link between variation in patterns of gene expression and variation in higher order traits such as neuropharmacological responses and patterns of behavior. Here we illustrate an approach that combines gene expression data with new bioinformatics resources to discover genes that potentially modulate behavior. We have exploited three complementary genetic models to obtain convergent evidence that differential expression of a subset of genes and molecular pathways influences ethanol-induced conditioned taste aversion (CTA). As a first step, cDNA microarrays were used to compare gene expression profiles of two null mutant mouse lines with difference in ethanol-induced aversion. Mice lacking a functional copy of G protein-gated potassium channel subunit 2 (Girk2) show a decrease in the aversive effects of ethanol, whereas preproenkephalin (Penk) null mutant mice show the opposite response. We hypothesize that these behavioral differences are generated in part by alterations in expression downstream of the null alleles. We then exploited the WebQTL databases to examine the genetic covariance between mRNA expression levels and measurements of ethanol-induced CTA in BXD recombinant inbred (RI) strains. Finally, we identified a subset of genes and functional groups associated with ethanol-induced CTA in both null mutant lines and BXD RI strains. Collectively, these approaches highlight the phosphatidylinositol signaling pathway and identify several genes including protein kinase C beta isoform and preproenkephalin in regulation of ethanol- induced conditioned taste aversion. Our results point to the increasing potential of the convergent approach and biological databases to investigate genetic mechanisms of complex traits.

RAGE is the major receptor for the proinflammatory activity of HMGB1 in rodent macrophages

Abstract High-mobility group box chromosomal protein 1 (HMGB1) is a protein with both intranuclear functions and extracellular cytokine-like effects. In this report, we study possible candidate receptors for HMGB1 on macrophages (Mphi) and define pathways activated by HMGB1 binding. Bone marrow Mphi were prepared from Dark Agouti (DA) rats and stimulated in vitro with HMGB1. The kinetics of tumour necrosis factor (TNF) production, NO production, activation of p38 mitogen-activated protein kinase (MAPK), p44/42 MAPK- and SAPK/JNK-signalling pathways, nuclear translocation of nuclear factor kappa B (NF-kappaB) and HMGB1-induced upregulation of major histocompatibility complex (MHC) class II and CD86 were analysed. Mphi from interleukin (IL)-1 receptor type I-/-, Toll-like receptor 2 (TLR2-/-) and RAGE-/- mice were used to investigate the role of these receptors in HMGB1 signalling. HMGB1 induced TNF and NO production by Mphi, phosphorylation of all investigated MAP kinase pathways and NF-kappaB translocation, and expression of MHC class II was increased. Mphi from RAGE-/- mice produced significantly lower amounts of TNF, IL-1beta and IL-6, while IL-1RI-/- and TLR2-/- Mphi produced cytokine levels comparable with wildtype controls in response to HMGB1 stimulation. We conclude that HMGB1 has the potential to induce a proinflammatory phenotype in Mphi, with RAGE as the major activation-inducing receptor.

Strains of coxsackie virus B4 differed in their ability to induce acute pancreatitis and the responses were negatively correlated to glucose tolerance

The outcome of infections with three CVB4 strains known to replicate in human pancreatic islet cells (E2, V89 4557 and VD2921) and one CVB3 strain (Nancy) in CBA/J mice with regard to viral replication, inflammation and glucose tolerance was studied. Isolation of virus from hearts, livers and pancreata was performed 7, 14 and 21 days post infection (pi). All strains could be equally well isolated from the pancreata and all but one strain, V89 4557, could be isolated from the hearts. The titers of neutralizing antibodies in the mice infected with the CVB4 strain V89 4557 were significantly lower than in mice infected with the other strains (p < 0.01). Even though virus was isolated from both heart and pancreata, immunohistochemical staining only revealed inflammatory cells in the latter. Seven days pi there was a significant difference between the strains in this respect i.e. mice infected with CVB3 and the E2 strain revealed more CD4+ lymphocytes, macrophages and granulocytes compared to mice infected with the other CBV strains (p < 0.05). Glucose tolerance tests performed at day 14 and at day 115 pi revealed normal kinetics of glucose absorption from the blood in the control mice and in mice infected with the strains that induced severe inflammation of the pancreas (E2 and CVB3). In contrast, the glucose clearance in mice infected with the CVB4 strains V89 4557 and VD2921 were significantly impaired compared to uninfected controls and compared to mice infected with the other CVB strains (p < 0.01). Mice infected with CVB4 strains V89 4557 also had a significantly impaired clearance of glucose 120 min after injection (p < 0.05) even though no virus could be isolated and no inflammation was detected in the pancreata at that time point. These results show that there is a clear strain difference with regard to the ability to affect clearance of glucose from the blood as late as 115 days pi as well as the degree of inflammation in the pancreas. This indicates that the in vitro diabetogenic strains (VD2921 and V89 4557) also in vivo can induce a pre-diabetic state in CBA/J mice.

Sum-frequency vibrational spectroscopy of chiral liquids off and close to electronic resonance and the antisymmetric Raman tensor

The strength of the chiral vibrational peaks in infrared-visible sum-frequency (SF) vibrational spectra from isotropic chiral liquids is proportional to the square of the corresponding antisymmetric Raman element. Under the Born-Oppenheimer adiabatic approximation with nonadiabatic corrections, the antisymmetric Raman tensor is much weaker than the symmetric counterpart, but becomes significantly stronger as the input frequency (or the sum-frequency in SF generation) approaches electronic resonance. We verify the theory with experimental results obtained from infrared-visible doubly resonant sum-frequency generation from an isotropic solution of chiral molecules.

A confidential study of deaths after emergency medical admission: issues relating to quality of care

In this retrospective pilot study we examine the feasibility of establishing a confidential enquiry into why some patients die after emergency admission to hospital. After excluding those who died in the first hour or who were admitted for palliative care, pairs of physicians were able to collect quantitative and qualitative data on 200 consecutive deaths. Both physicians reported shortfalls of care in 14 patients and one of the pair in 25 patients whose deaths would not have been the expected outcome. In 25, the shortfalls of care may have contributed to their deaths. Major problems were delays in seeing doctors, inaccurate diagnoses, delays in investigations and initiation of treatment. They occurred mostly in those admitted at night. It is possible that establishing the correct diagnosis and starting appropriate treatment may have been delayed in 64% of the 200 patients. The headline figures appear worse than some previous external assessment studies but this study did concentrate on those in whom problems were more likely. Nevertheless, the frequency is too high to be overlooked. In this feasibility study we have demonstrated that it is practicable for local staff to collect and assess data in hospitals and that the types of problems identified are relevant to anyone planning how to organise emergency care. A larger definitive study should be performed.

Transfected cells for study of alcohol actions on GABA(A) receptors

The ability to transfect and express foreign genes in cultured cells and Xenopus oocytes has contributed immensely to our knowledge of drug-receptor interactions and signal transduction following receptor activation. These techniques are now being used to study acute and chronic effects of ethanol on neurotransmitter receptors and cellular signaling. This article reviews the use of transfected cells to study ethanol actions on the GABAA receptor.

GABAA receptor alpha 1 and beta 2 subunit null mutant mice: behavioral responses to ethanol

Mice lacking either the alpha1 or beta 2 subunit of the GABAA receptor were tested for ethanol, saccharin, or quinine consumption, ethanol-conditioned place preference, ethanol-conditioned taste aversion, ethanol-simulated motor activity, and handling-induced seizures following chronic consumption of an ethanol liquid diet. The alpha1 null mutants showed decreased ethanol and saccharin consumption, increased aversion to ethanol, and a marked stimulation of motor activity after injection of ethanol. The beta 2 null mutants showed decreased consumption of saccharin and quinine, but not ethanol. Surprisingly, neither mutant showed marked changes in handling induced seizures before or after withdrawal of ethanol. The unique effects of deletion of these two GABAA receptor subunits on ethanol responses are discussed in terms of the distinct changes in different populations of GABAA receptors.

A pervasive mechanism for analgesia: activation of GIRK2 channels

G protein-coupled inwardly rectifying potassium channels (GIRKs) provide a common link between numerous neurotransmitter receptors and the regulation of synaptic transmission. We asked whether GIRKs specify a single behavioral action that is produced by drugs acting on the diverse receptors coupled with GIRKs. By using GIRK2-null mutant mice, we found marked reduction or complete elimination of the antinociceptive (hot plate test) effects of ethanol, oxotremorine, nicotine, baclofen, clonidine, and the cannabinoid receptor agonist WIN 55,212. However, ketamine analgesia remained intact. For most drugs, there was a sex difference in antinociceptive action, and the impact of deletion of the GIRK2 channel was less in female mice. The deletion of the GIRK2 channel blocks the opioid-dependent component of stress-induced analgesia (SIA), whereas nonopioid SIA was not changed. We propose that opioid, alpha adrenergic, muscarinic cholinergic, gamma-aminobutyric acid-B, and cannabinoid receptors are coupled with postsynaptic GIRK2 channels in vivo. Furthermore, this pathway accounts for essentially all of the antinociceptive effects in males, although females appear to recruit additional signal transduction mechanisms for some analgesic drugs.

Afterimages in fly motion vision

Afterimage-like effects modulate the responses of fly wide-field motion-sensitive cells following adaptation to stationary or slowly moving patterns. The origin of these afterimages is unclear. They have been interpreted as either the result of adaptation in the early visual system or as a direct consequence of the correlation scheme of motion detection. Using a combination of intracellular recording and computer modelling, we find that afterimage-like effects cannot be satisfactorily explained by a simple version of the correlation model previously proposed by Egelhaaf and Borst (J. Opt. Soc. Am. A 6 (1) (1989) 116). We propose a modified variant of the correlation model featuring a short delay filter and temporal high-pass filtering prior to motion correlation. Our model gives superior predictions of afterimage-like effects induced by a range of stimuli. Our model also predicts changes in cells' image step responses following exposure to motion, suggesting that previous experimental evidence for the "shortening delay" theory of motion adaptation (Biol. Cybern. 54 (1986) 223; Visual Neurosci. 14 (4) (1997) 741) should be re-interpreted in terms of afterimage effects.

Hyperactivity and dopamine D1 receptor activation in mice lacking girk2 channels

RATIONALE

G-protein-coupled inwardly rectifying potassium channels (GIRKs) regulate synaptic transmission and neuronal firing rates. Co-localization of GIRK2 channels and dopamine receptors in the mesolimbic system suggests a role in regulation of motor activity.

OBJECTIVES

To explore the role of GIRK channels in the regulation of motor behavior.

METHODS

GIRK2 null mutant mice (knockout) were used. Locomotor activity in a mildly stressful situation was conducted either in a circular open field with video tracking or in standard mouse cages equipped with infrared sensors. Drugs were injected intraperitoneally or subcutaneously.

RESULTS

GIRK2 knockout mice demonstrated a transient "hyperactive" behavioral phenotype with initially higher motor activity and slower habituation in a novel situation, increased levels of spontaneous locomotor activity during dark phase in their home cages, and impaired habituation in the open-field test. After habituation, GIRK2 knockout mice showed higher motor activity, which was inhibited by the D(1) receptor antagonist SCH 23390 and was more sensitive to the activating effects of the D(1) receptor partial agonist SKF 38393. In a novel environment (open-field) only the highest dose of SKF 38393 used (20 mg/kg) produced significant activation, perhaps due to a ceiling effect in GIRK2 knockout mice. SCH 23390 inhibited the basal activity levels of mice of both genotypes.

CONCLUSIONS

Activation of the dopamine D(1)receptor in a stressful environment may be stronger in GIRK2 deficient mice, and this modified function of D(1) receptors may cause the transient hyperactive behavioral phenotype of these mice.

Transgenic expression of a mutant glycine receptor decreases alcohol sensitivity of mice

Glycine receptors (GlyRs) are pentameric ligand-gated ion channels that inhibit neurotransmission in the adult brainstem and spinal cord. GlyR function is potentiated by ethanol in vitro, and a mutant GlyR subunit alpha(1)(S267Q) is insensitive to the potentiating effects of ethanol. To test the importance of GlyR for the actions of ethanol in vivo, we constructed transgenic mice with this mutation. Under the control of synapsin I regulatory sequences, transgenic expression of S267Q mutant GlyR alpha(1) subunits in the nervous system was demonstrated using [(3)H]strychnine binding and immunoblotting. These mice showed decreased sensitivity to ethanol in three behavioral tests: ethanol inhibition of strychnine seizures, motor incoordination (rotarod), and loss of righting reflex. There was no change in ethanol sensitivity in tests of acute functional tolerance or body temperature, and there was no change in ethanol metabolism. Transgene effects were pharmacologically specific for ethanol, compared with pentobarbital, flurazepam, and ketamine. These results support the idea that glycine receptors contribute to some behavioral actions of ethanol and that ethanol sensitivity can be changed in vivo by transgenic expression of a single receptor subunit.

Fc receptors are critical for autoimmune inflammatory damage to the central nervous system in experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is simulated by various forms of experimental autoimmune encephalomyelitis, in which T cells, antibodies, cytokines and complementary factors interact with the central nervous system (CNS) myelin proteins and lead to inflammatory damage. We investigated the role of Fc receptors (FcRs), which link the cellular and humoral branches of the immune system, in myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE), using two different FcRgamma knockout DBA/1 mice. The first knockout were the FcRgamma chain-deficient mice, which lack FcgammaRI, FcgammaRIII and Fc(epsilon)RI, while the second knockout mice lack only FcgammaRII. The lack of FcgammaRII enhanced the disease susceptibility with associated increased CNS demyelination. While FcRgamma+/+ DBA/1 mice also developed pronounced CNS infiltration and myelin destruction, FcRgamma-/- littermates were protected despite initial peripheral autoimmune responses to MOG. In vitro analyses revealed equivalent potentials of fluid phase phagocytosis of myelin and MOG in bone-marrow macrophages derived from both FcRgamma+/+ and FcRgamma-/- mice, while MOG-immunoglobulin (Ig)G immune complexes were only internalized by FcRgamma+/+ macrophages. This was associated with cellular activation in FcRgamma+/+ but not FcRgamma-/- macrophages, as assessed by the activation of intracellular mitogen activated protein (MAP)-kinase signalling elements. We propose that protection from EAE in FcRgamma-deficient mice is due to the inefficient antigen processing/presentation of myelin proteins during the induction of secondary immune responses locally in the CNS, which leads to demyelination. This demonstrates the importance of FcR in the promotion of autoimmune inflammation of the CNS and highlights the therapeutic possibility of treatment of MS with FcR-directed modalities.

Human skeletal muscle PDH kinase activity and isoform expression during a 3-day high-fat/low-carbohydrate diet

The increase in skeletal muscle pyruvate dehydrogenase kinase (PDK) activity was measured in skeletal muscle of six healthy males after a eucaloric high-fat/low-carbohydrate (HF/LC; 5% carbohydrate, 73% fat, and 22% protein of total energy intake) diet compared with a standardized prediet (50% carbohdyrate, 30% fat, and 21% protein). Biopsies were obtained from the vastus lateralis muscle after 3 days on the prediet (day 0) and after 1, 2, and 3 days of the HF/LC diet. Intact mitchondria were extracted from fresh muscle and analyzed for PDK activity and Western blotting of PDK2 and PDK4 protein. A second biopsy was taken at each time point and frozen for Northern blot analysis of PDK2 and PDK4 mRNAs. PDK activity increased in a linear fashion over the 3-day HF/LC diet and was significantly higher than control by 1 day. PDK activity was 0.09 +/- 0.03, 0.18 +/- 0.05, 0.30 +/- 0.07, and 0.37 +/- 0.09 min(-1) at 0, 1, 2, and 3 days, respectively. PDK4 protein and mRNA increased maximally by day 1, and PDK2 protein and mRNA were unaffected by the HF/LC diet. Resting respiratory exchange ratios decreased after 1 day of the HF/LC diet (from 0.79 +/- 0.02 to 0.72 +/- 0.02) and remained depressed throughout the 3-day dietary intervention (0.68 +/- 0.01). The immediate shift to fat utilization was accompanied by increased blood glycerol, beta-hydroxybutyrate, and plasma free fatty acid concentrations. These results suggest that the continuing increase in PDK activity over the 3-day HF/LC diet is not due to increasing PDK protein beyond 1 day. This could be due to the contribution of another isoform to the total PDK activity or to a continual increase in PDK4 or PDK2 specific activity.

Decision analysis of prenatal testing for chromosomal disorders: what do the preferences of pregnant women tell us?

Current guidelines recommend offering invasive testing for chromosomal disorders only to women who are aged 35 or older, or who are at similarly elevated risk (as determined by maternal serum and/or ultrasonographic screening). We conducted a decision analysis, using preference scores obtained from pregnant women, to determine whether current guidelines maximize the health-related quality of life of these women. If only miscarriage and chromosomal abnormalities are considered, the expected value of testing exceeds that of not testing for women 30 years of age or older. However, if a comprehensive range of relevant testing outcomes is considered, testing offers a higher expected value than not testing, regardless of age. Furthermore, patient preferences for specific testing outcomes play a much more substantial role in determining the course of action with the highest expected value than does the probability of any of the possible testing outcomes. The current age- and risk-based guideline for prenatal diagnosis does not maximize expected value and fails to appropriately consider individual patient preferences. For counseling purposes, how an individual values the presence and timing of fetal chromosomal information should be carefully understood.

Luciferase as a model for the site of inhaled anesthetic action

The in vivo potencies of anesthetics correlate with their capacity to suppress the reaction of luciferin with luciferase. In addition, luciferin has structural resemblances to etomidate. These observations raise the issues of whether luciferin, itself, might affect anesthetic requirement, and whether luciferase resembles the site of anesthetic action. Because the polar luciferin is unlikely to cross the blood-brain barrier (we found that the olive oil/water partition coefficient was 100 +/- 36 x 10(-7)), we studied these issues in rats by measuring the effect of infusion of luciferin in artificial cerebrospinal fluid into the lumbar subarachnoidal space and into the cerebral intraventricular space on the MAC (the minimum alveolar anesthetic concentration required to eliminate movement in response to a noxious stimulus in 50% of tested subjects) of isoflurane. MAC in rats given lumbar intrathecal doses of luciferin estimated to greatly exceed anesthetizing doses of etomidate, did not differ significantly from MAC in rats receiving only artificial cerebrospinal fluid into the lumbar intrathecal space. MAC slightly decreased when doses of luciferin estimated to greatly exceed anesthetizing doses of etomidate were infused intraventricularly (P < 0.05). In contrast to the absent or minimal effects of luciferin, intrathecal or intraventricular infusion of etomidate at similar or smaller doses significantly decreased isoflurane MAC. Luciferin did not affect +-aminobutyric acid type A or acetylcholine receptors expressed in Xenopus oocytes. These results suggest that luciferin has minimal or no anesthetic effects. It also suggests that luciferin/luciferase may not provide a good surrogate for the site at which anesthetics act, if this site is on the surface of neuronal cells.

IMPLICATIONS

In proportion to their potencies, anesthetics inhibit luciferin's action on luciferase, and luciferin structurally resembles the anesthetic etomidate. However, in contrast to etomidate, luciferin given intrathecally or into the third cerebral ventricle does not have anesthetic actions, and it does not affect +-aminobutyric acid or acetylcholine receptors in vitro. Luciferase may not provide a good surrogate for the site at which anesthetics act.

Adaptive increase in pyruvate dehydrogenase kinase 4 during starvation is mediated by peroxisome proliferator-activated receptor alpha

Pyruvate dehydrogenase kinase isoform 4 (PDK4) is upregulated by starvation in many tissues of the body during starvation. This causes inactivation of the pyruvate dehydrogenase complex which blocks pyruvate oxidation and conserves lactate and alanine for gluconeogenesis. Enhanced PDK4 expression may be caused by the increase in free fatty acids that occurs during starvation. Free fatty acids can activate peroxisome proliferator-activated receptor alpha (PPARalpha), and activation of PPARalpha can promote PDK4 expression. This model is supported by the findings reported here that WY-14,643, a synthetic PPARalpha activator, increases PDK4 expression in wild-type mice but not in PPARalpha-null mice. Starvation likewise increases the expression of PDK4 in tissues of wild-type mice but not in tissues of PPARalpha-null mice. These findings document the functional importance of PPARalpha for PDK4 expression during starvation and suggest an important role for elevated free fatty acids in the induction.

GIRK2 deficient mice. Evidence for hyperactivity and reduced anxiety

G-protein activated inwardly rectifying potassium channel (GIRK2)-deficient (null mutant) mice were examined in three tests for anxiety: the elevated plus-maze, light/dark box and "canopy" test. In the elevated plus-maze test, GIRK2 null mutant mice spent a higher percentage of time in the open arms and showed a higher number of total entries. A short (6 days) period of social isolation decreased anxiety and also increased the total activity in GIRK2 mutant mice. However, the increase of total activity in GIRK2 null mutant mice was mostly due to an increase in the number of entries into the open arms. The behavior of the wild-type animals was not substantially changed after social isolation. In the light/dark box, GIRK2 homozygous (-/-) mice demonstrated a higher level of locomotion and a higher number of rearings in the light area. In the "canopy" test, GIRK2 mutant mice displayed an increased locomotion in the exposed area and a strong trend to decrease in the number of stretched attend postures (SAP) in the most secure "canopy" area. GIRK2 heterozygous (+/-) animals showed behavioral changes intermediate between wild-type and null mutants only in the elevated plus-maze test after social isolation. In all other tests, GIRK2 heterozygous (+/-) animals did not differ from wild-type mice. Taken together, this data demonstrates that GIRK2 null mutant mice have reduced anxiety with signs of hyperactivity. We suggest that the functional block of dopamine D3 receptors may be a reason for this phenotype.

Regulation of branched-chain amino acid catabolism: nutritional and hormonal regulation of activity and expression of the branched-chain alpha-keto acid dehydrogenase kinase

Branched-chain alpha-keto acid dehydrogenase kinase is responsible for the inactivation and phosphorylation of the branched-chain alpha-keto acid dehydrogenase complex, the enzyme that catalyses the committed step of branched-chain amino acid catabolism. The activity of the branched-chain alpha-keto acid dehydrogenase complex is inversely correlated with kinase activity, suggesting that the relative activity of the kinase is the primary regulator of the activity of the complex. It has been shown that kinase activity and expression are affected by nutritional states imposed by low-protein diet feeding, starvation, diabetes, and exercise. Evidence has also been presented that certain hormones, particularly insulin, glucocorticoid, thyroid hormone and female sex hormones, affect the activity and expression of the kinase. The findings indicate that nutritional and hormonal control of the activity and expression of branched-chain alpha-keto acid dehydrogenase kinase provides an important means of control of the activity of the branched-chain alpha-keto acid dehydrogenase complex, with inactivation serving to conserve branched-chain amino acids for protein synthesis in some situations and activation serving to provide carbon for gluconeogenesis in others.

Potassium channels as targets for ethanol: studies of G-protein-coupled inwardly rectifying potassium channel 2 (GIRK2) null mutant mice

G-Protein-coupled inwardly rectifying potassium channels (GIRKs) regulate synaptic transmission and neuronal firing rates. Selective enhancement of GIRK2 function by intoxicating concentrations of ethanol was recently shown for recombinant homomeric and heteromeric channels. We proposed that specific behavioral actions of ethanol are due to activation of GIRK channels and that these behaviors would be reduced or eliminated in GIRK2 null mutant ("knockout") mice. Three behavioral effects of ethanol were absent in mutant mice as compared with wild-type littermates: stimulation of home cage (habituated) motor activity, anxiolytic action in elevated-plus maze test, and handling-induced convulsions (HIC) after an acute injection of ethanol. In contrast to these reductions of ethanol action, mutant mice displayed greater ethanol-stimulated activity in peripheral regions of an open field. There were no differences between mutant and wild-type mice for ethanol-induced sleep time, acute functional tolerance, or HIC following chronic matched consumption of a liquid diet. Ethanol preference and consumption were equal for wild-type and mutant mice using the standard two-bottle choice test with alternation of the bottles. However, this test was complicated by the strong side preference of the mice. When ethanol was presented constantly in their favored location, the consumption of ethanol was substantially higher for mutant than for wild-type mice. In the absence of ethanol, GIRK2 knockout mice showed more motor activity, less anxiety, and higher HIC. These results provide evidence that GIRK2 channels mediate specific behaviors, including anxiety and convulsions, and may influence effects of ethanol on these behaviors.

Differential effects of general anesthetics on G protein-coupled inwardly rectifying and other potassium channels

BACKGROUND

General anesthetics differentially affect various families of potassium channels, and some potassium channels are suggested to be potential targets for anesthetics and alcohols.

METHODS

The voltage-gated (ERG1, ELK1, and KCNQ2/3) and inwardly rectifying (GIRK1/2, GIRK1/4, GIRK2, IRK1, and ROMK1) potassium channels were expressed in Xenopus oocytes. Effects of volatile agents [halothane, isoflurane, enflurane, F3 (1-chloro-1,2,2-trifluorocyclobutane), and the structurally related nonimmobilizer F6 (1,2-dichlorohexafluorocyclobutane)], as well as intravenous (pentobarbital, propofol, etomidate, alphaxalone, ketamine), and gaseous (nitrous oxide) anesthetics and alcohols (ethanol and hexanol) on channel function were studied using a two-electrode voltage clamp.

RESULTS

ERG1, ELK1, and KCNQ2/3 channels were either inhibited slightly or unaffected by concentrations corresponding to twice the minimum alveolar concentrations or twice the anesthetic EC50 of volatile and intravenous anesthetics and alcohols. In contrast, G protein-coupled inwardly rectifying potassium (GIRK) channels were inhibited by volatile anesthetics but not by intravenous anesthetics. The neuronal-type GIRK1/2 channels were inhibited by 2 minimum alveolar concentrations of halothane or F3 by 45 and 81%, respectively, whereas the cardiac-type GIRK1/4 channels were inhibited only by F3. Conversely, IRK1 and ROMK1 channels were completely resistant to all anesthetics tested. Current responses of GIRK2 channels activated by mu-opioid receptors were also inhibited by halothane. Nitrous oxide (approximately 0.6 atmosphere) slightly but selectively potentiated GIRK channels. Results of chimeric and multiple amino acid mutations suggest that the region containing the transmembrane domains, but not the pore-forming domain, may be involved in determining differences in anesthetic sensitivity between GIRK and IRK channels.

CONCLUSIONS

G protein-coupled inwardly rectifying potassium channels, especially those composed of GIRK2 subunits, were inhibited by clinical concentrations of volatile anesthetics. This action may be related to some side effects of these agents.

Crystal structure of thiamin pyrophosphokinase

Thiamin pyrophosphate (TPP) is a coenzyme derived from vitamin B1 (thiamin). TPP synthesis in eukaryotes requires thiamin pyrophosphokinase (TPK), which catalyzes the transfer of a pyrophosphate group from ATP to thiamin. TPP is essential for central metabolic processes, including the formation of acetyl CoA from glucose and the Krebs cycle. Deficiencies in human thiamin metabolism result in beriberi and Wernicke encephalopathy. The crystal structure of mouse TPK was determined by multiwavelength anomalous diffraction at 2.4 A resolution, and the structure of TPK complexed with thiamin has been refined at 1.9 A resolution. The TPK polypeptide folds as an alpha/beta-domain and a beta-sandwich domain, which share a central ten-stranded mixed beta-sheet. TPK subunits associate as a dimer, and thiamin is bound in the dimer interface. Despite lacking apparent sequence homology with other proteins, the alpha/beta-domain resembles the Rossman fold and is similar to other kinase structures, including another pyrophosphokinase and a thiamin biosynthetic enzyme. Comparison of mouse and yeast TPK structures reveals differences that could be exploited in developing species-specific inhibitors of potential use as antimicrobial agents.

Anesthetics and ion channels: molecular models and sites of action

The mechanisms of general anesthesia in the central nervous system are finally yielding to molecular examination. As a result of research during the past several decades, a group of ligand-gated ion channels have emerged as plausible targets for general anesthetics. Molecular biology techniques have greatly accelerated attempts to classify ligand-gated ion channel sensitivity to general anesthetics, and have identified the sites of receptor subunits critical for anesthetic modulation using chimeric and mutated receptors. The experimental data have facilitated the construction of tenable molecular models for anesthetic binding sites, which in turn allows structural predictions to be tested. In vivo significance of a putative anesthetic target can now be examined by targeted gene manipulations in mice. In this review, we summarize from a molecular perspective recent advances in our understanding of mechanisms of action of general anesthetics on ligand-gated ion channels.