The anesthetic potency of propanol and butanol versus propanethiol and butanethiol in alpha1 wild type and alpha1(S267Q) glycine receptors

Although similar in shape and size, and although differing only by substitution of a sulfur atom for an oxygen atom, propanethiol and butanethiol differ markedly from propanol and butanol in their in vivo potency and physical properties. Recent theories of narcosis suggest that anesthetics may act by enhancing the effect of inhibitory agonists, such as glycine, on their receptors. We tested whether propanol, butanol, propanethiol, and butanethiol enhance the effect of glycine on alpha1 glycine receptors expressed in Xenopus laevis oocytes in a manner that reflects the in vivo differences found for potencies. As anticipated, we found an immediate parallel between in vivo (rat minimum alveolar concentration of anesthetic required to eliminate movement in response to a noxious stimulus in 50% of subjects) and in vitro (recombinant receptor) effects. All four compounds enhanced the effect of glycine on wild type receptors, and the extent of enhancement for a given minimum alveolar concentration-multiple was approximately the same for all compounds. We also found that propanethiol, butanethiol, propanol, and butanol did not affect, or minimally affected, the action of glycine in anesthetic resistant mutants in which the amino acid serine at position 267 was replaced by glutamine [alpha1(S267Q)].

IMPLICATIONS

The in vivo potencies of propanethiol, butanethiol, propanol, and butanol correlate with their capacities to enhance the effect of glycine on alpha1 glycine receptors expressed in Xenopus laevis oocytes. These results support the notion that a protein mediates anesthetic action.

The anesthetic potencies of alkanethiols for rats: relevance to theories of narcosis

Meyer and Overton suggested that anesthetic potency correlates inversely with lipophilicity. Thus, MAC times the olive oil/gas partition coefficient equals an approximately constant value of 1.82 +/- 0.56 atm (mean +/- SD). MAC is the minimum alveolar concentration of anesthetic required to eliminate movement in response to a noxious stimulus in 50% of subjects. Although MAC times the olive oil/gas partition coefficient also equals an approximately constant value for normal alkanols from methanol through octanol, the value (0.156 +/- 0.072 atm) is 1/10th that found for conventional anesthetics. We hypothesized that substitution of sulfur for the oxygen in n-alkanols would decrease their saline/gas partition coefficients (i.e., decrease polarity) while sustaining lipid/gas partition coefficients. Further, we hypothesized that these changes would produce products of MAC times olive oil partition coefficients that approximate those of conventional anesthetics. To test these predictions, we measured MAC in rats, and saline and olive oil solubilities for the series H(CH(2))(n)SH, comparing the results with the series H(CH(2))(n)OH for compounds having three to six carbon atoms. As hypothesized, the alkanethiols had similar oil/gas partition coefficients, 1000-fold smaller saline gas partition coefficients, and MAC values 30 times greater than for comparable alkanols. Such findings are consistent with the notion that the greater potency of many alkanols (greater than would be predicted from conventional inhaled anesthetics and the Meyer-Overton hypothesis) results from their greater polarity.

IMPLICATIONS

The in vivo anesthetic potency of alkanols and alkanethiols correlates with their lipophilicity and hydrophilicity.

Contrast gain reduction in fly motion adaptation

In many species, including humans, exposure to high image velocities induces motion adaptation, but the neural mechanisms are unclear. We have isolated two mechanisms that act on directionally selective motion-sensitive neurons in the fly's visual system. Both are driven strongly by movement and weakly, if at all, by flicker. The first mechanism, a subtractive process, is directional and is only activated by stimuli that excite the neuron. The second, a reduction in contrast gain, is strongly recruited by motion in any direction, even if the adapting stimulus does not excite the cell. These mechanisms are well designed to operate effectively within the context of motion coding. They can prevent saturation at susceptible nonlinear stages in processing, cope with rapid changes in direction, and preserve fine structure within receptive fields.

Selective modification of the pyruvate dehydrogenase kinase isoform profile in skeletal muscle in hyperthyroidism: implications for the regulatory impact of glucose on fatty acid oxidation

The pyruvate dehydrogenase kinases (PDK1-4) regulate glucose oxidation through inhibitory phosphorylation of the pyruvate dehydrogenase complex (PDC). Immunoblot analysis with antibodies raised against recombinant PDK isoforms demonstrated changes in PDK isoform expression in response to experimental hyperthyroidism (100 microg/100 g body weight; 3 days) that was selective for fast-twitch vs slow-twitch skeletal muscle in that PDK2 expression was increased in the fast-twitch skeletal muscle (the anterior tibialis) (by 1. 6-fold; P<0.05) but not in the slow-twitch muscle (the soleus). PDK4 protein expression was increased by experimental hyperthyroidism in both muscle types, there being a greater response in the anterior tibialis (4.2-fold increase; P<0.05) than in the soleus (3.2-fold increase; P<0.05). The hyperthyroidism-associated up-regulation of PDK4 expression was observed in conjunction with suppression of skeletal-muscle PDC activity, but not suppression of glucose uptake/phosphorylation, as measured in vivo in conscious unrestrained rats (using the 2-[(3)H]deoxyglucose technique). We propose that increased PDK isoform expression contributes to the pathology of hyperthyroidism and to PDC inactivation by facilitating the operation of the glucose --> lactate --> glucose (Cori) and glucose --> alanine --> glucose cycles. We also propose that enhanced relative expression of the pyruvate-insensitive PDK isoform (PDK4) in skeletal muscle in hyperthyroidism uncouples glycolytic flux from pyruvate oxidation, sparing pyruvate for non-oxidative entry into the tricarboxylic acid (TCA) cycle, and thereby supporting entry of acetyl-CoA (derived from fatty acid oxidation) into the TCA cycle.

Effects of gaseous anesthetics nitrous oxide and xenon on ligand-gated ion channels. Comparison with isoflurane and ethanol

BACKGROUND

Ligand-gated ion channels are considered to be potential general anesthetic targets. Although most general anesthetics potentiate the function of gamma-aminobutyric acid receptor type A (GABAA), the gaseous anesthetics nitrous oxide and xenon are reported to have little effect on GABAA receptors but inhibit N-methyl-d-aspartate (NMDA) receptors. To define the spectrum of effects of nitrous oxide and xenon on receptors thought to be important in anesthesia, the authors tested these anesthetics on a variety of recombinant brain receptors.

METHODS

The glycine, GABAA, GABA receptor type C (GABAC), NMDA, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA), kainate, 5-hydroxytryptamine3 (5-HT3), and nicotinic acetylcholine (nACh) receptors were expressed in Xenopus oocytes and effects of nitrous oxide and xenon, and as equipotent concentrations of isoflurane and ethanol, were studied using the two-electrode voltage clamp.

RESULTS

Nitrous oxide (0.58 atmosphere [atm]) and xenon (0.46 atm) exhibited similar effects on various receptors. Glycine and GABAA receptors were potentiated by gaseous anesthetics much less than by isoflurane, whereas nitrous oxide inhibited GABAC receptors. Glutamate receptors were inhibited by gaseous anesthetics more markedly than by isoflurane, but less than by ethanol. NMDA receptors were the most sensitive among glutamate receptors and were inhibited by nitrous oxide by 31%. 5-HT3 receptors were slightly inhibited by nitrous oxide. The nACh receptors were inhibited by gaseous and volatile anesthetics, but ethanol potentiated them. The sensitivity was different between alpha4beta2 and alpha4beta4 nACh receptors; alpha4beta2 receptors were inhibited by nitrous oxide by 39%, whereas alpha4beta4 receptors were inhibited by 7%. The inhibition of NMDA and nACh receptors by nitrous oxide was noncompetitive and was slightly different depending on membrane potentials for NMDA receptors, but not for nACh receptors.

CONCLUSIONS

Nitrous oxide and xenon displayed a similar spectrum of receptor actions, but this spectrum is distinct from that of isoflurane or ethanol. These results suggest that NMDA receptors and nACh receptors composed of beta2 subunits are likely targets for nitrous oxide and xenon.

Enhancement of natural killer (NK) cell cytotoxicity and induction of NK cell-derived interferon-gamma (IFN-gamma) display different kinetics during experimental infection with Trypanosoma cruzi

Early immunological activation involves an initial phase of cytokine activity and involvement of cell types such as NK cells. Such early immune responses are often decisive in resolution of microbial infection. NK cells reduce parasitaemia and enhance survival in experimental Trypanosoma cruzi infection, although the nature of these protective effects is not well understood. In this study, a detailed analysis of innate cytokine induction in the absence and presence of NK cells during the first 8 days of infection was performed. Following intraperitoneal infection with a high dose of parasites, reverse transcriptase-polymerase chain reaction showed that splenic mRNA for IFN-gamma appeared as a peak 24 h after infection and then reappeared 2-3 days later. In NK-depleted animals the first peak of IFN-gamma was absent and the second wave was slightly delayed. mRNA for IL-12 and tumour necrosis factor-alpha (TNF-alpha) as well as IFN-alpha protein in serum was only recorded 24 h after infection, at the same time as the IFN-gamma peak. NK depletion resulted in a small decrease of IL-12 mRNA levels, whereas TNF-alpha and IFN-alpha were not affected. NK cytotoxicity remained elevated throughout the 8 days and thus did not parallel the expression of IFN-gamma production by NK cells. We conclude that NK cell cytokine production and cytolytic activity play different roles in response to challenge with T. cruzi.

Starvation increases the amount of pyruvate dehydrogenase kinase in several mammalian tissues

Covalent modification of the pyruvate dehydrogenase complex provides an important regulatory mechanism for controlling the disposal of glucose and other compounds metabolized to pyruvate. Regulation of the complex by this mechanism is achieved in part by tissue-specific expression of the genes encoding isoenzymes of pyruvate dehydrogenase kinase (PDK). Starvation is known from our previous work to increase PDK activity of heart and skeletal muscle by increasing the amount of PDK isoenzyme 4 (PDK4) present in these tissues. This study demonstrates that increased expression of both PDK4 and PDK2 occurs in rat liver, kidney, and lactating mammary gland in response to starvation. PDK4 and PDK2 message levels were also increased by starvation in the two tissues examined (liver and kidney), suggesting enhancement of gene transcription. Changes in PDK2 message and protein were of similar magnitude, but changes in PDK4 message were greater than those in PDK4 protein, suggesting regulation at the level of translation. In contrast to these tissues, starvation had little or no effect on PDK2 and PDK4 protein in brain, white adipose tissue, and brown adipose tissue. Nevertheless, PDK4 message levels were significantly increased in brain and white adipose tissue by starvation. The findings of this study indicate that increased expression of PDK isoenzymes is an important mechanism for bringing about inactivation of the pyruvate dehydrogenase complex during starvation in many but not all tissues of the body. The absence of this mechanism preserves the capacity of neuronal tissue to utilize glucose for energy during starvation.

Fibrin sealant foam sprayed directly on liver injuries decreases blood loss in resuscitated rats

OBJECTIVE

The majority of early trauma deaths are attributable to uncontrolled hemorrhage from truncal sites. A hemorrhage-control technique that reduced bleeding in the prehospital phase of treatment without requiring manual compression may improve the outcome of these patients. We conducted this preliminary study to determine whether an expanding fibrin sealant foam (FSF) would reduce bleeding from a severe liver injury even during resuscitation.

METHODS

Rats (n = 31; 291 +/- 5 g; 37.4 +/- 0.3 degrees C; mean +/- SEM), underwent a 60 +/- 5% excision of the median hepatic lobe. The animals received one of three treatments: (1) FSF, (2) immunoglobulin G placebo foam (IgGF), or (3) no treatment. All animals were resuscitated with 40 degrees C lactated Ringer's solution at 3.3 mL/ min/kg to a mean arterial pressure of 100 mm Hg. Total blood loss, mean arterial pressure, and resuscitation volume were recorded for 30 minutes. A qualitative measure of foam coverage and adherence to the cut liver edge was recorded.

RESULTS

The total blood loss was less (p < 0.01) in the FSF group (21.2 +/- 5.0 mL/kg) than in either IgGF (41.4 +/- 4.3 mL/kg) or the no treatment group (44.6 +/- 4.7 mL/kg), which did not differ. The resuscitation volume was not different. The amount of foam used in the treated groups, 9.1 +/- 1.0 g in the FSF group and 10.0 +/- 1.0 g in the IgGF group, did not differ. Survival for 30 minutes was not different among groups. There was no difference in the amount of cut liver covered by either foam, but the clots were more adherent (p < 0.05) in the FSF group than in the IgGF group.

CONCLUSION

In rats with a severe liver injury, spraying fibrin foam directly on the cut liver surface decreased blood loss when compared with placebo foam and no treatment. This pilot study suggests a future possible treatment for noncompressible truncal hemorrhage.

Specific binding sites for alcohols and anesthetics on ligand-gated ion channels

Ligand-gated ion channels are a target for inhaled anesthetics and alcohols in the central nervous system. The inhibitory strychnine-sensitive glycine and gamma-aminobutyric acid type A receptors are positively modulated by anesthetics and alcohols, and site-directed mutagenesis techniques have identified amino acid residues important for the action of volatile anesthetics and alcohols in these receptors. A key question is whether these amino acids are part of an alcohol/anesthetic-binding site. In the present study, we used an alkanethiol anesthetic to covalently label its binding site by mutating selected amino acids to cysteine. We demonstrated that the anesthetic propanethiol, or alternatively, propyl methanethiosulfonate, covalently binds to cysteine residues introduced into a specific second transmembrane site in glycine receptor and gamma-aminobutyric acid type A receptor subunits and irreversibly enhances receptor function. Moreover, upon permanent occupation of the site by propyl disulfide, the usual ability of octanol, enflurane, and isoflurane to potentiate the function of the ion channels was lost. This approach provides strong evidence that the actions of anesthetics in these receptors are due to binding at a single site.

Behavioural changes produced by transgenic overexpression of gamma2L and gamma2S subunits of the GABAA receptor

Transgenic mice overexpressing either the mouse gamma2L or gamma2S subunit of the GABAA receptor were generated in a C57BL/6 J x DBA/2 J mixed background and expanded into transgenic lines. Transgenic mice and littermate controls were analysed with respect to altered behaviour indicative of anxiety, motor activity and acute effects of benzodiazepines and alcohol, as well as with regard to altered responses to alcohol withdrawal and acute functional tolerance to alcohol. Biochemical tests assessed flunitrazepam- and ethanol-enhanced 36Cl- flux stimulated by muscimol in cerebellar and cortical microsacs and [3H]-flunitrazepam binding to cerebellar membranes. There were no significant differences in any of these measures between the transgenic and control mice, except in tests of acute functional tolerance to acute injection of ethanol. Compared to controls, mice carrying either the gamma2L or gamma2S transgene developed significantly less tolerance to the ataxic effects of ethanol. We conclude that acute functional tolerance to ethanol is very sensitive to the amount of GABAA receptor gamma2 subunit available (regardless of whether it is gamma2L or gamma2S) but overexpression of neither subunit isoform alters other behavioural and biochemical phenotypes.

Rescue of gamma2 subunit-deficient mice by transgenic overexpression of the GABAA receptor gamma2S or gamma2L subunit isoforms

The gamma2 subunit is an important functional determinant of GABAA receptors and is essential for formation of high-affinity benzodiazepine binding sites and for synaptic clustering of major GABAA receptor subtypes along with gephyrin. There are two splice variants of the gamma2 subunit, gamma2 short (gamma2S) and gamma2 long (gamma2L), the latter carrying in the cytoplasmic domain an additional eight amino acids with a putative phosphorylation site. Here, we show that transgenic mice expressing either the gamma2S or gamma2L subunit on a gamma2 subunit-deficient background are phenotypically indistinguishable from wild-type. They express nearly normal levels of gamma2 subunit protein and [3H]flumazenil binding sites. Likewise, the distribution, number and size of GABAA receptor clusters colocalized with gephyrin are similar to wild-type in both juvenile and adult mice. Our results indicate that the two gamma2 subunit splice variants can substitute for each other and fulfil the basic functions of GABAA receptors, allowing in vivo studies that address isoform-specific roles in phosphorylation-dependent regulatory mechanisms.

Targeted upregulation of pyruvate dehydrogenase kinase (PDK)-4 in slow-twitch skeletal muscle underlies the stable modification of the regulatory characteristics of PDK induced by high-fat feeding

In using Western blot analysis with antibodies raised against recombinant pyruvate dehydrogenase kinase (PDK) isoforms PDK2 and PDK4, this study demonstrates selective PDK isoform switching in specific skeletal muscle types in response to high-fat feeding that is associated with altered regulation of PDK activity by pyruvate. The administration of a diet high in saturated fats led to stable (approximately 2-fold) increases in PDK activities in both a typical slow-twitch (soleus [SOL]) muscle and a typical fast-twitch (anterior tibialis [AT]) muscle. Western blot analysis revealed that high-fat feeding significantly increased (approximately 2-fold; P < 0.001) PDK4 protein expression in SOL, with a modest (1.3-fold) increase in PDK2 protein expression. The relative increase in PDK4 protein expression in SOL was associated with a 7.6-fold increase in the pyruvate concentration that was required to elicit a 50% active pyruvate dehydrogenase complex, which indicates a marked decrease in the sensitivity of PDK to inhibition by pyruvate. In AT muscle, high-fat feeding elicited comparable (1.5- to 1.7-fold) increases (P < 0.05) in PDK4 and PDK2 protein expression. Loss of sensitivity of PDK to inhibition by pyruvate was less marked. The data suggest that a positive correlation exists between increases in PDK4 expression and the propensity with which muscles use lipid-derived fuels as respiratory substrates rather than with the degree of insulin resistance induced in skeletal muscles by high-fat feeding. In conclusion, high-fat feeding leads to selective upregulation of PDK4 expression in slow-twitch muscle in response to high-fat feeding in vivo, which is associated with a pronounced loss of sensitivity of PDK activity to acute inhibition by pyruvate. Thus, increased PDK4 expression may underlie the stable modification of the regulatory characteristics of PDK observed in slow-twitch muscle in response to high-fat feeding.

Subunit-dependent inhibition of human neuronal nicotinic acetylcholine receptors and other ligand-gated ion channels by dissociative anesthetics ketamine and dizocilpine

Background The neuronal mechanisms responsible for dissociative anesthesia remain controversial. N-methyl-D-aspartate (NMDA) receptors are inhibited by ketamine and related drugs at concentrations lower than those required for anesthetic effects. Thus, the authors studied whether ligand-gated ion channels other than NMDA receptors might display a sensitivity to ketamine and dizocilpine that is consistent with concentrations required for anesthesia.

METHODS

Heteromeric human neuronal nicotinic acetylcholine receptors (hnAChR channels alpha2beta2, alpha2beta4, alpha3beta2, alpha3beta4, alpha4beta2 and alpha4beta4), 5-hydroxytryptamine3 (5-HT3), alpha1beta2gamma2S gamma-aminobutyric acid type A (GABAA) and alpha1 glycine receptors were expressed in Xenopus oocytes, and effects of ketamine and dizocilpine were studied using the two-electrode voltage-clamp technique.

RESULTS

Both ketamine and dizocilpine inhibited hnAChRs in a noncompetitive and voltage-dependent manner. Receptors containing beta1 subunits were more sensitive to ketamine and dizocilpine than those containing beta2 subunits. The inhibitor concentration for half-maximal response (IC50) values for ketamine of hnAChRs composed of beta4 subunits were 9.5-29 microM, whereas those of beta2 subunits were 50-92 microM. Conversely, 5-HT3 receptors were inhibited only by concentrations of ketamine and dizocilpine higher than the anesthetic concentrations. This inhibition was mixed (competitive/noncompetitive). GABAA and glycine receptors were very resistant to dissociative anesthetics.

CONCLUSIONS

Human nAChRs are inhibited by ketamine and dizocilpine at concentrations possibly achieved in vivo during anesthesia in a subunit-dependent manner, with beta subunits being more critical than alpha subunits. Conversely, 5-HT3, GABAA, and glycine receptors were relatively insensitive to dissociative anesthetics.

Fibre-type specific modification of the activity and regulation of skeletal muscle pyruvate dehydrogenase kinase (PDK) by prolonged starvation and refeeding is associated with targeted regulation of PDK isoenzyme 4 expression

Using immunoblot analysis with antibodies raised against recombinant pyruvate dehydrogenase kinase (PDK) isoenzymes PDK2 and PDK4, we demonstrate selective changes in PDK isoenzyme expression in slow-twitch versus fast-twitch skeletal muscle types in response to prolonged (48 h) starvation and refeeding after starvation. Starvation increased PDK activity in both slow-twitch (soleus) and fast-twitch (anterior tibialis) skeletal muscle and was associated with loss of sensitivity of PDK to inhibition by pyruvate, with a greater effect in anterior tibialis. Starvation significantly increased PDK4 protein expression in both soleus and anterior tibialis, with a greater response in anterior tibialis. Starvation did not effect PDK2 protein expression in soleus, but modestly increased PDK2 expression in anterior tibialis. Refeeding for 4 h partially reversed the effect of 48-h starvation on PDK activity and PDK4 expression in both soleus and anterior tibialis, but the response was more marked in soleus than in anterior tibialis. Pyruvate sensitivity of PDK activity was also partially restored by refeeding, again with the greater response in soleus. It is concluded that targeted regulation of PDK4 isoenzyme expression in skeletal muscle in response to starvation and refeeding underlies the modulation of the regulatory characteristics of PDK in vivo. We propose that switching from a pyruvate-sensitive to a pyruvate-insensitive PDK isoenzyme in starvation (a) maintains a sufficiently high pyruvate concentration to ensure that the glucose-->alanine-->glucose cycle is not impaired, and (b) may 'spare' pyruvate for anaplerotic entry into the tricarboxylic acid cycle to support the entry of acetyl-CoA derived from fatty acid (FA) oxidation into the tricarboxylic acid cycle. We further speculate that FA oxidation by skeletal muscle is both forced and facilitated by upregulation of PDK4, which is perceived as an essential component of the operation of the glucose-FA cycle in starvation.

Experimental hyperthyroidism causes inactivation of the branched-chain alpha-ketoacid dehydrogenase complex in rat liver

Hyperthyroidism induced by 3-day treatment of rats with thyroid hormone (T(3); 3,5,3'-triiodothyronine) at 0.1 or 1 mg/kg body wt/day resulted in a reduced activity state (% of enzyme in its active, dephosphorylated state) of the hepatic branched-chain alpha-ketoacid dehydrogenase (BCKDH) complex. One treatment with 0.1 mg T(3)/kg body wt caused a significant effect on the activity state of BCKDH complex after 24 h, indicating that the reduction of the activity state was triggered by the first administration of T(3). Hyperthyroidism also caused a stable increase in BCKDH kinase activity, the enzyme responsible for phosphorylation and inactivation of the BCKDH complex, suggesting that T(3) caused inactivation of the BCKDH complex by induction of its kinase. Western blot analysis also revealed increased amounts of BCKDH kinase protein in response to hyperthyroidism. No change in the plasma levels of branched-chain alpha-keto acids was observed in T(3)-treated rats, arguing against an involvement of these known regulators of BCKDH kinase activity. Inactivation of the hepatic BCKDH complex as a consequence of overexpression of its kinase may save the essential branched-chain amino acids for protein synthesis during hyperthyroidism.

Interferon-gamma induces secretion of trypanosome lymphocyte triggering factor via tyrosine protein kinases

Bidirectional signalling between Trypanosoma brucei brucei and CD8+ T cells involves reciprocal action of the parasite-derived trypanosome derived lymphocyte triggering factor (TLTF) and lymphocyte-derived IFN-gamma. Herein we further characterize this relationship and report quantitation of TLTF secretion into culture supernatants using a newly developed ELISA. Secretion is induced by IFN-gamma in a dose-response manner, with 100 U/ml giving maximal yields of bioactive TLTF as assessed by ELISA and ELISPOT. This is a constitutive and active secretion. Furthermore, IFN-gamma-induced secretion was dependent on tyrosine protein kinase activity. Specific blockers of this signalling system resulted in lower yields of TLTF in the culture supernatants.

Visualization of inhibitory Ly49 receptor specificity with soluble major histocompatibility complex class I tetramers

Murine natural killer (NK) cells are inhibited from killing their targets by the interaction between inhibitory, C-type lectin like Ly49 receptors and major histocompatibility complex (MHC) class I molecules. The receptors have overlapping specificity, and it has been difficult to analyze specific aspects of the interaction between different Ly49 receptors and their respective ligands. We have addressed this problem using tetramers of bacterially expressed, non-glycosylated, MHC class I molecules refolded with different peptides. Our results indicate that this technology is useful for analysis of Ly49 receptor specificity as well as for monitoring of NK cell subsets, with the following major conclusions emerging from this study: (1) tetramers of H-2D(d) bound the Ly49A receptor; the MHC associated glycan, previously suggested to be involved in recognition by this receptor, is thus not required for Ly49A receptor binding; (2) in support and extension of a recent report indicating peptide selectivity in the recognition of H-2K(b) by Ly49C(+) cells, H-2K(b) tetramer binding to Ly49C receptors was strongly influenced by the peptide presented by the MHC class I molecule; (3) tetramer binding allowed visualization of interactions that have not previously been detected in functional studies, such as the recognition of H-2D(b) by Ly49A and Ly49C.

G-protein-coupled inwardly rectifying potassium channels are targets of alcohol action

G-protein-coupled inwardly rectifying potassium channels (GIRKs) are important for regulation of synaptic transmission and neuronal firing rates. Because of their key role in brain function, we asked if these potassium channels are targets of alcohol action. Ethanol enhanced function of cerebellar granule cell GIRKs coupled to GABAB receptors. Enhancement of GIRK function by ethanol was studied in detail using Xenopus oocytes expressing homomeric or heteromeric channels. Function of all GIRK channels was enhanced by intoxicating concentrations of ethanol, but other, related inwardly rectifying potassium channels were not affected. GIRK2/IRK1 chimeras and GIRK2 truncation mutants were used to identify a region of 43 amino acids in the carboxyl (C) terminus that is critical for the action of ethanol on these channels.

Human neuronal nicotinic acetylcholine receptors expressed in Xenopus oocytes predict efficacy of halogenated compounds that disobey the Meyer-Overton rule

BACKGROUND

According to the Meyer-Overton rule, anesthetic potency of a substance can be predicted by its lipid solubility, but a group of halogenated volatile compounds predicted to induce anesthesia does not obey this rule. Thus, these compounds are useful tools for studies of molecular targets of anesthetics. Human neuronal nicotinic acetylcholine receptor (hnAChR) subunits have been recently cloned, which allowed the authors to assess whether these receptors could differentiate among volatile anesthetic and nonimmobilizer compounds. This study provides the first data regarding anesthetic sensitivity of hnAChRs.

METHODS

alpha2beta4, alpha3beta4, and alphaabeta2 hnAChRs were expressed in Xenopus oocytes, and effects of volatile anesthetics isoflurane and F3 (1-chioro-1,2,2-triflurocyclobutane, 1A) and nonimmobilizers F6 (1,2-dichlorohexafluorocyclobutane, 2N) and F8 (2,3-dichlorooctafluorobutane) on the peak acetylcholine-gated currents were studied using the two-electrode voltage-clamp technique.

RESULTS

Isoflurane and F3 inhibited all the hnAChRs tested in a concentration-dependent manner. Isoflurane at a concentration corresponding to 1 minimum alveolar concentration (MAC) inhibited 83, 69, and 71% of ACh-induced currents in alpha2beta4, alpha3beta4, and alpha4beta2 hnAChRs, respectively, and 1 MAC of F3 inhibited 64, 44, and 61% of currents gated in those receptors. F6 (8-34 microM) did not cause any changes in currents gated by any of the receptors tested. F8 (4-18 microM) did not alter the currents gated in either alpha3beta4 or alpha4beta2 receptors, but caused a small potentiation of alpha2beta4 hnAChRs without a concentration-response relation.

CONCLUSION

The in vivo potency and effectiveness of volatile anesthetic and nonimmobilizer compounds were consistent with their actions on hnAChRs expressed in a recombinant expression system, suggesting a potential participation of these receptors in the mechanisms of anesthesia.

Ethanol actions on multiple ion channels: which are important?

BACKGROUND

This review is based on a plenary lecture presented at the 1999 meeting of the Research Society on Alcoholism. It provides an overview of the search for sites of action for ethanol in the brain. Initial studies were directed at interaction of ethanol with membrane lipids, but during the past decade, emphasis has been shifted to protein sites, particularly those on ion channels. Molecular biological techniques have provided the opportunity to study isolated channels in cellular expression systems and also provide the opportunity to manipulate these channels in mutant mice.

CONCLUSIONS

There is now compelling evidence that multiple ion channels are affected by ethanol and growing support for the idea that ethanol interacts directly with specific sites on ion channels. The key, and unanswered, question is which of these channels are responsible for alcohol-induced behaviors such as intoxication, tolerance, dependence, or craving. Mutant mice will likely give (some) answers to these questions during the next decade.

Amino acid volume and hydropathy of a transmembrane site determine glycine and anesthetic sensitivity of glycine receptors

Two specific amino acid residues in transmembrane segments (TM) 2 and 3 are critical for the enhancement of glycine receptor (GlyR) function by volatile anesthetics. To determine which physicochemical characteristics of these sites determine their roles in anesthetic actions, an extensive series of single amino acid mutations at amino acid residue 288 (Ala-288) in TM3 of the alpha1 GlyR subunit was tested for modulation by volatile anesthetics. The mutations changed the apparent affinities of receptors for glycine; replacements with larger volumes and less hydropathy exhibited higher affinities for glycine. Potentiation by anesthetics was reduced by specific mutations at Ala-288. The molecular volume of the substituents was negatively correlated with the extent of potentiation by isoflurane, enflurane, and 1-chloro-1,2,2-trifluorocyclobutane, whereas there was no correlation between anesthetic enhancement and polarity, hydropathy, or hydrophilicity of substituents. In contrast to anesthetics, no correlation was found between the effects of the nonanesthetics 1,2-dichlorohexafluorocyclobutane or 2, 3-dichlorooctafluorobutane and any physicochemical property of the substituent. These results suggest that the molecular volume and hydropathy of the amino acid at position 288 in TM3 regulate glycine and anesthetic sensitivity of the GlyR and that this residue might represent one determinant of an anesthetic binding site.

Mechanism responsible for inactivation of skeletal muscle pyruvate dehydrogenase complex in starvation and diabetes

Regulation of the activity of the pyruvate dehydrogenase complex in skeletal muscle plays an important role in fuel selection and glucose homeostasis. Activation of the complex promotes disposal of glucose, whereas inactivation conserves substrates for hepatic glucose production. Starvation and diabetes induce a stable increase in pyruvate dehydrogenase kinase activity in skeletal muscle mitochondria that promotes phosphorylation and inactivation of the complex. The present study shows that these metabolic conditions induce a large increase in the expression of PDK4, one of four pyruvate dehydrogenase kinase isoenzymes expressed in mammalian tissues, in the mitochondria of gastrocnemius muscle. Refeeding starved rats and insulin treatment of diabetic rats decreased pyruvate dehydrogenase kinase activity and also reversed the increase in PDK4 protein in gastrocnemius muscle mitochondria. Starvation and diabetes also increased the abundance of PDK4 mRNA in gastrocnemius muscle, and refeeding and insulin treatment again reversed the effects of starvation and diabetes. These findings suggest that an increase in amount of this enzyme contributes to hyperphosphorylation and inactivation of the pyruvate dehydrogenase complex in these metabolic conditions. It was further found that feeding rats WY-14,643, a selective agonist for the peroxisome proliferator-activated receptor-alpha (PPAR-alpha), also induced large increases in pyruvate dehydrogenase kinase activity, PDK4 protein, and PDK4 mRNA in gastrocnemius muscle. Since long-chain fatty acids activate PPAR-alpha endogenously, increased levels of these compounds in starvation and diabetes may signal increased expression of PDK4 in skeletal muscle.

Dry fibrin sealant dressings reduce blood loss, resuscitation volume, and improve survival in hypothermic coagulopathic swine with grade V liver injuries

OBJECTIVE

The majority of early trauma deaths are caused by uncontrolled hemorrhage, and are frequently complicated by hypothermic and dilutional coagulopathies. Any hemorrhage-control technique that achieves rapid hemostasis despite a coagulopathy should improve the outcome of these patients. We conducted this study to determine whether dry fibrin sealant dressings (DFSD) would stop bleeding from grade V liver injuries in swine that were hypothermic and coagulopathic.

METHODS

Nineteen swine weighing 39.7 kg (mean and 95% confidence interval, 36.3-43.1), underwent a 60% isovolemic, hypothermic exchange transfusion with 33 degrees C 6% hetastarch to produce a dilutional and hypothermic coagulopathy. The animals then received a grade V liver injury and one of three treatments: DFSD, conventional liver packing with gauze sponges, or immunoglobulin G (IgG) placebo sealant dressing (blinded control). All animals were resuscitated with lactated Ringer's solution to their preinjury mean arterial pressure. Blood loss after treatment, mean arterial pressure, resuscitation volume, hematologic variables, and core temperature were monitored for 1 hour.

RESULTS

At the time of injury, core temperature = 33.3 degrees C (95% confidence interval, 33.2-33.4), hemoglobin concentration = 4.4 g/dL (4.2-4.6), platelet count = 132 x 10(5)/microL, (93-171), prothrombin time = 21.6 seconds (19.6-23.5), activated partial thromboplastin time = 25.2 seconds (range, 22.9-27.5 seconds), and fibrinogen = 83 mg/dL (range, 76-89 mg/dL) across treatments. The posttreatment blood loss in the DFSD group was 669 mL, (range, 353-1,268 mL), which was lower (p < 0.01) than the means of 3,321 mL (range, 1,891-5,831 mL) and 4,399 mL (range, 2,321-8,332 mL) observed in the packing and IgG groups, respectively. The resuscitation volume in DFSD was 2,145 mL (range 1,310-3,514 mL), which was lower (p < 0.05) than the means of 5,222 mL (range 3,381-8,067 mL) and 5,542 mL (range 3,384-9,077 mL) in the packing and IgG groups, respectively. One-hour survival in the DFSD group was 83%, whereas survival in the packing and IgG groups were 0% (p < 0.05).

CONCLUSION

In swine with a grade V liver injury complicated by a dilutional and hypothermic coagulopathy, DFSD provided simple, rapid hemorrhage control, decreased fluid requirements, and improved survival.