[The relationship between insulin resistance and risk of long-term mortality in people without diabetes: a 30-year follow-up of the Daqing Diabetes Study].

Objective: To determine whether insulin resistance is associated with all-cause mortality in subjects without diabetes. Methods: A total of 505 participants without diabetes, 198 with normal glucose tolerance (NGT) and 307 with impaired glucose tolerance (IGT), were recruited from the Daqing Diabetes Study. The participants were followed up for 30 years. They were stratified into three groups (tertiles) according to baseline homeostasis model assessment of insulin resistance(HOMA-IR) levels, as the HOMA-IR 0, the HOMA-IR 1 and the HOMA-IR 2 groups, to assess the predictive effect of insulin resistance on risk of all-cause mortality. Results: During the 30-year follow-up, 52, 56 and 78 participants died across the three HOMA-IR groups, respectively. The corresponding mortality per 1 000 person-years (95%CI) were 12.12 (9.56-15.01), 13.10 (10.46-16.03) and 19.91 (16.73-23.15), respectively. Participants in the HOMA-IR 2 group had a significantly higher risk of death than those in the HOMA-IR 0 group after adjustment of age, sex and smoking status (HR=1.97,95%CI 1.38-2.81, P<0.001). Cox analyses showed that a one standard deviation increase in HOMA-IR was associated with a 22% increase in the mortality after adjustment of potential confounders (HR=1.22, 95%CI 1.08-1.39, P=0.002). Conclusions: Insulin resistance is associated with increased risk of all-cause death in Chinese people without diabetes, suggesting that improving insulin resistance could be beneficial for people without diabetic in reducing risk of long-term all-cause mortality.

[Association between physical activity and risk of stroke among adults aged 40 years and above: a prospective cohort study].

Objective: To examine the effect of physical activity (PA) on the incident risk of stroke among adults aged 40 years and above. Methods: The baseline data including PA and demographic characteristics were obtained from the Adult Chronic Disease Surveillance with population representativeness in Ningbo in 2015. The follow-up data of interested health outcomes from 2015 to 2019 were retrieved from a population-based Integrated Noncommunicable Disease Collaborative Management System in Ningbo. The two databases were matched to form a queue. PA was divided into three levels of low-intensity, moderate-intensity, and vigorous-intensity according to the metabolic equivalents (METs) spent per week. Cox regression model was used to calculate the hazard ratio (HR) and 95% confidence interval. Results: A total of 3 353 subjects were included at baseline survey in 2015. Until Dec 31, 2019, there had been 31 stroke events had occurred since then, with accumulative incidence rate of 242/100 000, and an average follow-up time of (50.28±2.54) months. When adjusted for gender, age, education level, smoking status, alcohol consumption, BMI and hypertension, multivariate Cox regression analysis showed that greater PA was associated with a 37.9% reduction of incidence of stroke (HR=0.621,95%CI:0.393-0.983). Compared with those who had low-intensity PA, those who were with vigorous-intensity. PA appeared associated with a 63.1% decrease in the incidence of stroke (HR=0.369, 95%CI: 0.139-0.976). However, there was no statistical significance with moderate-intensity PA (HR=0.712,95%CI:0.323-1.569), noticed. Conclusions: Greater PA is likely to reduce the incidence of stroke. Our findings indicated that people should be encouraged to increase the PA level and developing a healthy supportive environment in the community.

[Subjects with impaired glucose tolerance returned to normal glucose status for six years had lower long-term risk of diabetes: 20 years follow up of Daqing diabetes prevention study].

Objective: To explore the influence of lifestyle intervention on long-term diabetes in subjects with impaired glucose tolerance (IGT) returned to normal glucose tolerance (NGT) within 6 years. Methods: A total of 577 subjects (aged 25-74 years old) with IGT in Daqing were enrolled and randomly assigned to control, and diet, exercise and diet plus exercise groups in a six-year intervention trial in 1986. Subjects who were non-diabetic at the end of the intervention were followed up for additional 14 years. Results: Among all the subjects, 41.38% of them who had returned to NGT from IGT within 6 years maintained NGT status after 20 years, and had a lower incidence of diabetes than subjects maintained IGT status (46.55% vs. 75.25%). Of note, in the intervention group, the percentage of participants developed diabetes in the NGT subjects was significantly lower than that in the IGT group (43.71% vs. 76.25%) after 20 years. There was high long-term risk for diabetes in the IGT subjects after the adjustment of age, sex and baseline glucose (HR=1.81, 95%CI 1.27-2.58, P=0.001), whereas in the non-intervention group, no significant difference could be viewed in long-term diabetic risk between subjects maintained IGT status and those returned to NGT (71.43% vs. 65.22%) after adjusting of the same confounders (HR=1.03, 95%CI 0.45-2.35, P=0.94). Conclusions: IGT subjects who had returned to NGT in early years had lower risk for future diabetes than those who remained IGT. However, this beneficial effect could only be viewed in the intervention group, but not in the non-intervention group.

Detection of genuine tripartite entanglement and steering in hybrid optomechanics.

Multipartite quantum entanglement is a key resource for ensuring security in quantum network. We show that by using a unified parameter in terms of reduced noise variances one can determine different types of tripartite entanglement of a given state generated in a hybrid optomechanical system, where an atomic ensemble is located inside a single-mode cavity with a movable mirror, with different thresholds for each type. In particular, the special quantum states which allow both entanglement and steering genuinely shared among atom-light-mirror modes can be observed, even though there is no direct interaction between the mirror and the atomic ensemble. We further show the robustness against mechanical thermal noise and damping, the relaxation time of atomic ensemble, as well as the effect of gain factors involved in the criteria. Our analysis provides an experimentally achievable method to determine the type of tripartite quantum correlation in a way.

Efficient Scheme for Perfect Collective Einstein-Podolsky-Rosen Steering.

A practical scheme for the demonstration of perfect one-sided device-independent quantum secret sharing is proposed. The scheme involves a three-mode optomechanical system in which a pair of independent cavity modes is driven by short laser pulses and interact with a movable mirror. We demonstrate that by tuning the laser frequency to the blue (anti-Stokes) sideband of the average frequency of the cavity modes, the modes become mutually coherent and then may collectively steer the mirror mode to a perfect Einstein-Podolsky-Rosen state. The scheme is shown to be experimentally feasible, it is robust against the frequency difference between the modes, mechanical thermal noise and damping, and coupling strengths of the cavity modes to the mirror.

Icariin decreases both APP and Aß levels and increases neurogenesis in the brain of Tg2576 mice.

Icariin is derived most commonly from the traditional Chinese herb Epimedium brevicornum Maxim. Our previous studies have shown that icariin protects neurons from neurotoxic and ischemic conditions. This study aims to investigate the effect of icariin on the expression of amyloid precursor protein (APP) and the level of amyloid-ß peptide (Aß), as well as neurogenesis in the brain of Tg2576 mice, an animal model of Alzheimer's disease (AD). Tg2576 mice and wild-type littermates (WT) were randomized into the following three groups: Tg2576, Tg2576+icariin, and WT groups. All 9-month-old mice were treated with icariin (60mg/kg/d) or distilled water for 3months. Following this, the spatial working memory of Tg2576+icariin mice, as examined in the Y-maze task, was found to improve. Furthermore, reduced levels of insoluble Aß1-40 (69%) and Aß1-42 (50%) after icariin treatment were determined in the brain by enzyme-linked immunosorbent assay (ELISA). Western blot analysis indicated the downregulation of APP expression after icariin treatment, and double staining showed an increased number of 5-bromo-2-deoxyuridine (BrdU)/Neuron-specific nuclear protein (NeuN) double-positive cells in the dentate gyrus region of the hippocampus in Tg2576+icariin mice compared with the Tg2576 mice. The current study demonstrated that icariin improved memory function, decreased the levels of Aß and APP in the brain, and enhanced neurogenesis in the hippocampus of Tg2576 mice. Collectively, these results suggest the potential therapeutic value of icariin in AD.

Classifying directional Gaussian entanglement, Einstein-Podolsky-Rosen steering, and discord.

Using Venn diagrams, we classify the different types of two-mode Gaussian continuous variable quantum correlation including directional entanglement and Einstein-Podolsky-Rosen (EPR) steering. We establish unified signatures for one- and two-way quantum steering, entanglement, and discord beyond entanglement in terms of an EPR-type variance. By focusing on Gaussian states, we link an optimized condition for entanglement based on an EPR variance to the Simon-Peres condition. This allows us to quantify the asymmetry of the Gaussian entanglement, and to relate the asymmetry to a directional quantum teleportation protocol where Alice and Bob possess asymmetrically noisy channels. Our analysis enables a determination of the type and direction of quantum correlation in a way that is easily measured in experiment. We also find that for symmetric states, when discord exceeds a certain threshold, the states are necessarily steerable.

High aspect ratio SiNW arrays with Ag nanoparticles decoration for strong SERS detection.

Well-ordered silicon nanowires (SiNWs) are applied as surface-enhanced Raman scattering (SERS) substrates. Laser interference lithography is used to fabricate large-area periodic nanostructures. By controlling the reaction time of metal assisted chemical etching, various aspect ratios of SiNWs are generated. Ag nanoparticles are decorated on the substrates via redox reaction to allow a good coverage of Ag over the SiNWs. As the height of the SiNWs increases, the light scattering inside the structures is enhanced. The number of the probing molecules within the detection volume is increased as well. These factors contribute to stronger light-matter interaction and thus lead to higher SERS signal intensity. However, the light trapping effect is more significant for higher SiNWs, which prevents the detection of the SERS signals. An optimized aspect ratio ∼5:1 (1 µm height and 200 nm width) for the SiNW array is found. The well-ordered SiNWs demonstrate better SERS signal intensity and uniformity than the randomly arranged SiNWs.

Characteristic spectrum of very low-energy photoelectron from above-threshold ionization in the tunneling regime.

We report an experimental and theoretical study of very low-energy photoelectrons in tunneling ionization process from noble gas atoms interacting with ultrashort intense infrared laser pulses. A universal peak structure with electron energy well below 1 eV in the photoelectron spectrum, corresponding to the double-hump structure in the longitudinal momentum distribution, is identified experimentally for all atomic species. Our quantum and semiclassical analysis reveal the role of long-range Coulomb potential in the production of this very low-energy peak structure.

Progesterone withdrawal increases the anxiolytic actions of gaboxadol: role of alpha4betadelta GABA(A) receptors.

Hippocampal alpha4betadelta GABA(A) receptors (GABA(A)-R) are increased following progesterone withdrawal (PWD) in a rodent model of premenstrual anxiety. This alpha4betadelta receptor isoform uniquely responds to the GABA agonist gaboxadol (THIP) with a maximum current greater than that gated by GABA, and is potentiated more by pentobarbital than are other GABA(A)-R. We therefore investigated the anxiolytic effects of these drugs using the elevated plus maze. Gaboxadol (1.25 mg/kg) was markedly more anxiolytic in animals undergoing PWD than in controls. Pentobarbital (10 mg/kg) also produced a greater anxiolytic effect during PWD. These results suggest that the pharmacological properties of alpha4betadelta GABA(A)-R following PWD are evident behaviorally. Alterations in the alpha4betadelta GABA(A)-R population may have implications for the etiology and treatment of premenstrual syndrome.

Progesterone withdrawal increases the alpha4 subunit of the GABA(A) receptor in male rats in association with anxiety and altered pharmacology - a comparison with female rats.

Withdrawal from the neurosteroid 3alpha,5alpha-allopregnanolone after chronic administration of progesterone increases anxiety in female rats and up-regulates the alpha4 subunit of the GABA(A) receptor (GABA(A)-R) in the hippocampus. We investigated if these phenomena would also occur in male rats. Progesterone withdrawal (PWD) induced higher alpha4 subunit expression in the hippocampus of both male and female rats, in association with increased anxiety (assessed in the elevated plus maze) comparable to effects previously reported. Because alpha4-containing GABA(A)-R are insensitive to the benzodiazepine (BDZ) lorazepam (LZM), and are positively modulated by flumazenil (FLU, a BDZ antagonist), we therefore tested the effects of these compounds following PWD. Using whole-cell patch clamp techniques, LZM-potentiation of GABA ((EC20))-gated current was markedly reduced in CA1 pyramidal cells of male rats undergoing PWD compared to controls, whereas FLU had no effect on GABA-gated current in control animals but increased it in PWD animals. Behaviorally, both male and female rats were significantly less sensitive to the anxiolytic effects of LZM. In contrast, FLU demonstrated significant anxiolytic effects following PWD. These data suggest that neurosteroid regulation of the alpha4 GABA(A)-R subunit may be a relevant mechanism underlying anxiety disorders, and that this phenomenon is not sex-specific.

Short-term exposure to a neuroactive steroid increases alpha4 GABA(A) receptor subunit levels in association with increased anxiety in the female rat.

Previous work from this laboratory has demonstrated that withdrawal from the neuroactive steroid 3alpha,5alpha-THP (3alpha-hydroxy-5alpha-pregnan-20-one) after 3-week exposure to its parent compound, progesterone (P), increases anxiety and produces benzodiazepine (BDZ) insensitivity in female rats. These events were linked to upregulation of the alpha4 subunit of the GABA(A) receptor (GABAR) in the hippocampus [Brain Res. 507 (1998) 91; Nature 392 (1998) 926; J. Neurosci. 18 (1998) 5275]. The present study investigates the role of shorter term hormone treatment on alpha4 subunit levels as well as relevant behavioral and pharmacological end-points related to GABAR function. After 2-3 days of P exposure, two- to threefold increases in alpha4 protein levels were observed, which declined to control values after 5-6 days of hormone exposure. This effect was due to the GABA-modulatory metabolite of P, 3alpha,5alpha-THP. alpha4 upregulation was inversely correlated with BDZ potentiation of GABA-gated current, assessed using whole cell patch clamp techniques on acutely isolated hippocampal pyramidal cells. A near total BDZ insensitivity was observed by 2-3 days of hormone exposure in association with the maximal increase in alpha4 levels. Up-regulation of the alpha4 GABAR subunit was also reflected by an increase in anxiety in the elevated plus maze. A significant decrease in open arm entries was observed after 72-h exposure to P, an effect which recovered by 6 days of P treatment. As demonstrated in vitro, alpha4 upregulation also resulted in a relative insensitivity to the anxiolytic actions of BDZ. These results suggest that short-term exposure to 3alpha,5alpha-THP produces changes in GABAR subunit composition similar to those that occur after chronic exposure and withdrawal from the steroid.

Thirteen UDPglucuronosyltransferase genes are encoded at the human UGT1 gene complex locus.

The original novel UGT1 complex locus previously shown to encode six different UDP-glucuronosyltransferase (transferase) genes has been extended and demonstrated to specify a total of 13 isoforms. The genes are designated UGT1A1 through UGT1A13p with four pseudo ones. UGT1A2p and UGT1A11p through UGT1A13p have either nucleotide deletions or flawed TATA boxes and are therefore pseudo. In the 5' region of the locus, the 13 unique exons 1 are arranged in a tandem array with each having its own proximal TATA box element and, in turn, are linked to four common exons to allow for the independent transcriptional initiation to generate overlapping primary transcripts. Only the lead exon in the nine viable primary transcripts is predicted to undergo splicing to the four common exons generating mRNAs with identical 3' ends and transferase isozymes with an identical carboxyl terminus. The unique amino terminus specifies acceptor-substrate selection, and the common carboxyl terminus apparently specifies the interaction with the common donor substrate, UDP-glucuronic acid. In the extended region, the viable TATA boxes are either A(A)TgA(AA)T or AT14AT; in the original locus the element for UGT1A1 is A(TA)7A and TAATT/CAA(A) for all of the other genes. UGT1A1 specifies the critically important bilirubin transferase isoform. The relationships of the exons 1 to each other are as follows: UGT1A2p through UGT1A5 comprises a cluster A that is 87-92% identical, and UGT1A7 through UGT1A13p comprises a cluster B that is 67-91% identical. For the two not included in a cluster, UGT1A1 is more identical to cluster A at 60-63%, whereas UGT1A6 is identical by between 48% and 56% to all other unique exons. The locus was expanded from 95 kb to 218 kb. Extensive probing of clones beyond 218 kb with coding nucleotides for a highly conserved amino acid sequence present in all transferases was unable to detect other exons 1. The mRNAs are differentially expressed in hepatic and extrahepatic tissues. This locus is indeed novel, indicating the least usage of exon sequences in specifying different transferase isozymes that have an expansive substrate range.

The phenobarbital response enhancer module in the human bilirubin UDP-glucuronosyltransferase UGT1A1 gene and regulation by the nuclear receptor CAR.

The UDP-glucuronosyltransferase, UGT1A1, is the critical enzyme responsible for detoxification of the potentially neurotoxic bilirubin by conjugating it with glucuronic acid. For decades, phenobarbital (PB) treatment for hyperbilirubinemia has been known to increase expression of the UGT1A1 gene in liver. We have now delineated the PB response activity to a 290-bp distal enhancer sequence (-3483/-3194) of the UGT1A1 gene. The enhancer contains 3 putative nuclear receptor motifs, and it was activated by the nuclear orphan receptor, human constitutive active receptor (hCAR), in cotransfected HepG2 cells. Bacterially expressed hCAR, acting as a heterodimer with in vitro-translated retinoid X receptor (RXRalpha), only bound to 1 of the 3 NR motifs, named gtNR1 in a gel-shift assay. Consistently, mutations of the gtNR1 site significantly decreased the activation by hCAR of the 290-bp DNA in transfection assays. Moreover, the 290-bp DNA was effectively activated in mouse primary hepatocytes in response to PB, offering an excellent clinical test for the examination of the responsiveness of the UGT1A1 to PB in the human population, particularly individuals with hyperbilirubinemia.

Withdrawal from 3alpha-OH-5alpha-pregnan-20-One using a pseudopregnancy model alters the kinetics of hippocampal GABAA-gated current and increases the GABAA receptor alpha4 subunit in association with increased anxiety.

In the present study, we have characterized properties of steroid withdrawal using a pseudopregnant rat model. This paradigm results in increased production of endogenous progesterone from ovarian sources and as such is a useful physiological model. "Withdrawal" from progesterone induced by ovariectomy on day 12 of pseudopregnancy resulted in increased anxiety, as determined by a decrease in open arm entries on the elevated plus maze compared to control rats and pseudopregnant animals not undergoing withdrawal. Similar findings were obtained 24 hr after administration of a 5alpha-reductase blocker to a pseudopregnant animal, suggesting that it is the GABAA-modulatory 3alpha-OH-5alpha-pregnan-20-one (3alpha, 5alpha-THP) that produces anxiogenic withdrawal symptoms. Twenty-four hours after steroid withdrawal, the time constant for decay of GABAA-gated current was also reduced sixfold, assessed using whole- cell patch-clamp procedures on pyramidal neurons acutely dissociated from CA1 hippocampus. Thus, 3alpha,5alpha-THP withdrawal results in a marked decrease in total GABAA current, a possible mechanism for its anxiogenic, proconvulsant sequelae. In addition, 3alpha,5alpha-THP withdrawal resulted in insensitivity to the normally potentiating effect of the benzodiazepine lorazepam (LZM) on GABAA-gated Cl- current. This withdrawal profile is similar to that reported for other GABAA-modulatory drugs such as the benzodiazepines (BDZs), barbiturates, and ethanol. These changes were also associated with significant two and threefold increases in both the mRNA and protein for the alpha4 subunit of the GABAA receptor, respectively, in hippocampus. The pseudopregnancy paradigm may be a useful model for periods of endogenous 3alpha,5alpha-THP withdrawal such as premenstrual syndrome and postpartum or postmenopausal dysphoria, when increased emotional lability and BDZ insensitivity have been reported.

GABA(A) receptor alpha4 subunit suppression prevents withdrawal properties of an endogenous steroid.

The hormone progesterone is readily converted to 3alpha-OH-5alpha-pregnan-20-one (3alpha,5alpha-THP) in the brains of males and females. In the brain, 3alpha,5alpha-THP acts like a sedative, decreasing anxiety and reducing seizure activity, by enhancing the function of GABA (gamma-aminobutyric acid), the brain's major inhibitory neurotransmitter. Symptoms of premenstrual syndrome (PMS), such as anxiety and seizure susceptibility, are associated with sharp declines in circulating levels of progesterone and, consequently, of levels of 3alpha,5alpha-THP in the brain. Abrupt discontinuation of use of sedatives such as benzodiazepines and ethanol can also produce PMS-like withdrawal symptoms. Here we report a progesterone-withdrawal paradigm, designed to mimic PMS and post-partum syndrome in a rat model. In this model, withdrawal of progesterone leads to increased seizure susceptibility and insensitivity to benzodiazepine sedatives through an effect on gene transcription. Specifically, this effect was due to reduced levels of 3alpha,5alpha-THP which enhance transcription of the gene encoding the alpha4 subunit of the GABA(A) receptor. We also find that increased susceptibility to seizure after progesferone withdrawal is due to a sixfold decrease in the decay time for GABA currents and consequent decreased inhibitory function. Blockade of the alpha4 gene transcript prevents these withdrawal properties. PMS symptoms may therefore be attributable, in part, to alterations in expression of GABA(A) receptor subunits as a result of progesterone withdrawal.

Essential role of NF-E2 in remodeling of chromatin structure and transcriptional activation of the epsilon-globin gene in vivo by 5' hypersensitive site 2 of the beta-globin locus control region.

Much of our understanding of the process by which enhancers activate transcription has been gained from transient-transfection studies in which the DNA is not assembled with histones and other chromatin proteins as it is in the cell nucleus. To study the activation of a mammalian gene in a natural chromatin context in vivo, we constructed a minichromosome containing the human epsilon-globin gene and portions of the beta-globin locus control region (LCR). The minichromosomes replicate and are maintained at stable copy number in human erythroid cells. Expression of the minichromosomal epsilon-globin gene requires the presence of beta-globin LCR elements in cis, as is the case for the chromosomal gene. We determined the chromatin structure of the epsilon-globin gene in both the active and inactive states. The transcriptionally inactive locus is covered by an array of positioned nucleosomes extending over 1,400 bp. In minichromosomes with a (mu)LCR or DNase I-hypersensitive site 2 (HS2) which actively transcribe the epsilon-globin gene, the nucleosome at the promoter is altered or disrupted while positioning of nucleosomes in the rest of the locus is retained. All or virtually all minichromosomes are simultaneously hypersensitive to DNase I both at the promoter and at HS2. Transcriptional activation and promoter remodeling, as well as formation of the HS2 structure itself, depended on the presence of the NF-E2 binding motif in HS2. The nucleosome at the promoter which is altered upon activation is positioned over the transcriptional elements of the epsilon-globin gene, i.e., the TATA, CCAAT, and CACCC elements, and the GATA-1 site at -165. The simple availability of erythroid transcription factors that recognize these motifs is insufficient to allow expression. As in the chromosomal globin locus, regulation also occurs at the level of chromatin structure. These observations are consistent with the idea that one role of the beta-globin LCR is to maintain promoters free of nucleosomes. The restricted structural change observed upon transcriptional activation may indicate that the LCR need only make a specific contact with the proximal gene promoter to activate transcription.

Similarities and differences in mechanisms of cardiotoxins, melittin and other myotoxins.

Myonecrosis induced in vivo by cardiotoxin, melittin, and Asp49 and Lys49 phospholipase A2 (PLA2) myotoxins involves rapid lysis of the sarcolemma, myofibril clumping, and hypercontraction of sarcomeres. In contrast, skeletal muscle necrosis induced by crotamine and myotoxin a is much slower, consisting of mitochondrial and sarcoplasmic reticulum swelling, myofibril degeneration, and lack of sarcolemma or transverse tubule damage. The mechanisms contributing to the myonecrosis induced by these peptides were evaluated. Two cardiotoxins and two Lys49 PLA2 myotoxins lysed primary cultures of human skeletal muscle within 24 hr at a concentration of 0.25 microM, while melittin, crotamine, and myotoxin a, and an Asp49 PLA2 myotoxin were non-cytolytic at concentrations up to 5.0 microM, suggesting that cytolysis is not a good measure of myotoxicity. Crotamine and the Lys49 PLA2 myotoxin altered Ca2+ ion flux in human heavy sarcoplasmic reticulum by opening the ryanocine receptor. Whole-cell patch-clamp studies demonstrated that administrating crotamine intracellularly increased Na+ currents. Free fatty acids, liberated by activation of tissue phospholipase C or by the PLA2 activity of the myotoxins, were monitored for crotamine, myotoxin a and a Lys49 PLA2 myotoxin in cell cultures in which the lipids had been radiolabeled. Only the Lys49 myotoxin produced significant amounts of fatty acid in cell cultures, supporting a potential role for fatty acid production only in the mechanism of sarcolemma-destroying myotoxins. These findings, coupled with those in the literature, support a hypothesis in which the myotoxins and/or products of lipase activity (e.g. fatty acids) are acting at a site existing on both the Na+ channel and a protein involved in Ca2+ release and probably serving a modulatory function for ion regulation. Based on the similarities in mechanisms between the toxins and fatty acids, the most likely site would be a fatty acid binding site on the protein (either similar to that on fatty acid binding proteins, or an acylated cysteine residue) or in the membrane.

Altered sodium current response to intracellular fatty acids in halothane-hypersensitive skeletal muscle.

Biopsies of human skeletal muscle were analyzed by an in vitro contracture test (IVCT) for responsiveness to a halothane challenge: noncontracting (nonresponsive; IVCT-) and contracting (IVCT+). A muscle biopsy that is IVCT+ indicates potential malignant hyperthermia (MH) susceptibility. Primary cultures were grown from portions of the skeletal muscle biopsies, and voltage-activated currents were measured by whole cell recording in the presence or absence of 2-5 microM intracellular arachidonic or oleic acids. In untreated IVCT- cells, Na+ currents were predominantly tetrodotoxin (TTX) insensitive, indicating that most of the current was carried through the embryonic SkM2 isoform of the Na+ channel. Inclusion of fatty acids in the recording pipette of IVCT- cells produced an increase in voltage-activated Na+ currents during 20 min of recording. Approximately 70% of currents in fatty acid-treated cells were TTX sensitive, indicating activation of the adult SkM1 isoform of the Na+ channel. In contrast to IVCT- cells, IVCT+ cells expressed Na+ currents that were predominantly TTX sensitive even in the absence of added fatty acid, thus showing a relatively large baseline functional expression of SkM1 channels. Addition of fatty acids to the recording pipette produced little further change in the magnitude or TTX sensitivity of the whole cell currents in IVCT+ cells, suggesting altered functional regulation of Na+ channels in MH muscle.