Metformin but not glyburide prevents high glucose-induced abnormalities in relaxation and intracellular Ca2+ transients in adult rat ventricular myocytes

We have recently demonstrated that adult rat ventricular myocytes maintained in a high glucose (HG) culture medium exhibit abnormalities in excitation-contraction coupling similar to myocytes from diabetic rats. Metformin, an insulin-sensitizing biguanide, enhances peripheral insulin action and lowers blood pressure in hyperinsulinemic animals, but its direct impact on cardiac function is not fully understood. To examine the role of metformin on HG-induced cardiac dysfunction at the cellular level, normal adult ventricular myocytes were cultured for 1 day in a serum-free insulin-containing medium with either normal glucose (5.5 mmol/l glucose) or HG (25.5 mmol/l glucose) in the presence or absence of metformin or the sulfonylurea glyburide. Mechanical properties were evaluated using a high-speed video-edge detection system, and intracellular Ca2+ transients were recorded in fura-2-loaded myocytes. As previously reported, culturing myocytes in HG depresses peak shortening, prolongs time to 90% relengthening, and slows Ca2+ transient decay. Culturing cells with metformin (50 micromol/l) prevented the HG-induced abnormalities in relaxation without ameliorating depressed peak-shortening amplitudes. Incubation of the cells with metformin also prevented slower intracellular Ca2+ clearing induced by HG. However, the HG-induced relaxation defects were not improved by glyburide (50-300 micromol/l). Interestingly, metformin also improved HG-induced relaxation abnormalities in the absence of insulin, whereas it failed to protect against HG in the presence of the tyrosine kinase inhibitor genistein (50 micromol/l). These data demonstrate that, unlike glyburide, metformin provides cardioprotection against HG-induced abnormalities in myocyte relaxation, perhaps through tyrosine kinase-dependent changes in intracellular Ca2+ handling, independent of its insulin sensitizing action.

Outcomes of primary phakic trabeculectomies without versus with 0.5- to 1-minute versus 3- to 5-minute mitomycin C

PURPOSE

To compare the intraocular pressure and hypotony outcomes of primary phakic trabeculectomies with no mitomycin C (MMC), shorter MMC, and longer MMC exposure.

METHODS

We evaluated primary phakic trabeculectomies with no MMC (36 eyes of 36 patients), 0.5- to 1-minute MMC (50 eyes of 50 patients), and 3- to 5-minute MMC (38 eyes of 38 patients) at the concentration of 0.5 mg/ml. Successful trabeculectomy was defined as an intraocular pressure of 21 mm Hg or less without development of a marked visual acuity loss associated with prolonged hypotony (intraocular pressure < 6 mm Hg over 3 months) and without the need for additional surgery to control intraocular pressure or treat postoperative complications.

RESULTS

The three groups were similar in demographics, preoperative intraocular pressure, and medical dependency. However, the incidence of hypotony during the postoperative periods of 3 to 12 months was significantly higher in the 3- to 5-minute MMC group (P < .05, chi-square test). Severe visual acuity loss associated with hypotony was also more frequently found in the 3- to 5-minute MMC group than in the 0.5- to 1-minute (P = .009, chi-square test) group or the control group (P = .014, chi-square test). In addition, the success probabilities were significantly different among the three groups (P = .001, Kaplan-Meier survival analysis with log-rank test) and were the highest in the 0.5- to 1-minute MMC group and the lowest in the 3- to 5-minute MMC group.

CONCLUSION

Shorter application (0.5 to 1 minute) of MMC appears to be optimal for the successful outcome of primary phakic trabeculectomy compared with no MMC or longer application of MMC at a concentration of 0.5 mg/ml.

Metallothionein alleviates cardiac contractile dysfunction induced by insulin resistance: role of Akt phosphorylation, PTB1B, PPARgamma and c-Jun

AIMS/HYPOTHESIS

Insulin resistance is concomitant with metabolic syndrome, oxidative stress and cardiac contractile dysfunction. However, the causal relationship between oxidative stress and cardiac dysfunction is unknown. This study was designed to determine the impact of overexpression of the cardiac antioxidant metallothionein on cardiac dysfunction induced by insulin resistance in mice.

METHODS

Whole-body insulin resistance was generated in wild-type FVB and metallothionein transgenic mice by feeding them with sucrose for 12 weeks. Contractile and intracellular Ca(2+) properties were evaluated in ventricular myocytes using an IonOptix system. The contractile indices analysed included: peak shortening (PS), time to 90% PS (TPS(90)), time to 90% relengthening (TR(90)), half-width duration, maximal velocity of shortening (+dL/dt) and relengthening (-dL/dt), fura-fluorescence intensity change (DeltaFFI) and decay rate (tau).

RESULTS

The sucrose-fed mice displayed glucose intolerance, enhanced oxidative stress, hyperinsulinaemia, hypertriglyceridaemia and normal body weight. Compared with myocytes in starch-fed mice, those from sucrose-fed mice exhibited depressed PS, +dL/dt, -dL/dt, prolonged TR(90) and decay rate, and reduced DeltaFFI associated with normal TPS(90) and half-width duration. Western blot analysis revealed enhanced basal, but blunted insulin (15 mU/g)-stimulated Akt phosphorylation. It also showed elevated expression of insulin receptor beta, insulin receptor tyrosine phosphorylation, peroxisome proliferator-activated receptor gamma, protein tyrosine phosphatase 1B and phosphorylation of the transcription factor c-Jun, associated with a reduced fold increase of insulin-stimulated insulin receptor tyrosine phosphorylation in sucrose-fed mice. All western blot findings may be attenuated or ablated by metallothionein.

CONCLUSIONS/INTERPRETATION

These data indicate that oxidative stress may play an important role in cardiac contractile dysfunction associated with glucose intolerance and possibly related to alteration in insulin signalling at the receptor and post-receptor levels.

Proinflammatory protein CARD9 is essential for infiltration of monocytic fibroblast precursors and cardiac fibrosis caused by Angiotensin II infusion

Background

Angiotensin II (Ang II)–induced cardiac remodeling with the underlying mechanisms involving inflammation and fibrosis has been well documented. Cytosolic adaptor caspase recruitment domain 9 (CARD9) has been implicated in the innate immune response. We aimed to examine the role of CARD9 in inflammation and cardiac fibrosis induced by Ang II.

Methods

Two-month-old CARD9-deficient (CARD9^−/−) and wild-type (WT) male mice were infused with Ang II (1,500 ng/kg/min) or saline for 7 days. Heart sections were stained with hematoxylin and eosin and Masson trichrome and examined by immunohistochemistry; and activity and protein levels were measured in macrophages obtained from mice.

Results

WT mice with Ang II infusion showed a marked increase in CARD9⁺ macrophages in the heart, but CARD9^−/− mice showed significantly suppressed macrophage infiltration and expression of proinflammatory cytokines, including interleukin-1β (IL-1β) and connective tissue growth factor (CTGF). Importantly, Ang II–induced cardiac fibrosis (extracellular matrix and collagen I deposition) was diminished in CARD9^−/− hearts, as was the expression of transforming growth factor-β (TGF-β) and level of myofibroblasts positive for α-smooth muscle actin (α-SMA). Furthermore, Ang II activation of nuclear factor-κB (NF-κB), JNK and p38 mitogen-activated protein kinases (MAPKs) in WT macrophages was reduced in CARD9^−/− macrophages.

Conclusion

CARD9 plays an important role in regulating cardiac inflammation and fibrosis in response to elevated Ang II.

Crystal structures of Zidovudine- or Lamivudine-resistant human immunodeficiency virus type 1 reverse transcriptases containing mutations at codons 41, 184, and 215

Six structures of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) containing combinations of resistance mutations for zidovudine (AZT) (M41L and T215Y) or lamivudine (M184V) have been determined as inhibitor complexes. Minimal conformational changes in the polymerase or nonnucleoside RT inhibitor sites compared to the mutant RTMC (D67N, K70R, T215F, and K219N) are observed, indicating that such changes may occur only with certain combinations of mutations. Model building M41L and T215Y into HIV-1 RT-DNA and docking in ATP that is utilized in the pyrophosphorolysis reaction for AZT resistance indicates that some conformational rearrangement appears necessary in RT for ATP to interact simultaneously with the M41L and T215Y mutations.

3'-Azido-3'-deoxythymidine drug resistance mutations in HIV-1 reverse transcriptase can induce long range conformational changes

HIV reverse transcriptase (RT) is one of the main targets for the action of anti-AIDS drugs. Many of these drugs [e.g., 3'-azido-3'-deoxythymidine (AZT) and 2',3'-dideoxyinosine (ddI)] are analogues of the nucleoside substrates used by the HIV RT. One of the main problems in anti-HIV therapy is the selection of a mutant virus with reduced drug sensitivity. Drug resistance in HIV is generated for nucleoside analogue inhibitors by mutations in HIV RT. However, most of these mutations are situated some distance from the polymerase active site, giving rise to questions concerning the mechanism of resistance. To understand the possible structural bases for this, the crystal structures of AZT- and ddI-resistant RTs have been determined. For the ddI-resistant RT with a mutation at residue 74, no significant conformational changes were observed for the p66 subunit. In contrast, for the AZT-resistant RT (RTMC) bearing four mutations, two of these (at 215 and 219) give rise to a conformational change that propagates to the active site aspartate residues. Thus, these drug resistance mutations produce an effect at the RT polymerase site mediated simply by the protein. It is likely that such long-range effects could represent a common mechanism for generating drug resistance in other systems.

2-Amino-6-arylsulfonylbenzonitriles as non-nucleoside reverse transcriptase inhibitors of HIV-1

A series of 2-amino-5-arylthiobenzonitriles (1) was found to be active against HIV-1. Structural modifications led to the sulfoxides (2) and sulfones (3). The sulfoxides generally showed antiviral activity against HIV-1 similar to that of 1. The sulfones, however, were the most potent series of analogues, a number having activity against HIV-1 in the nanomolar range. Structural-activity relationship (SAR) studies suggested that a meta substituent, particularly a meta methyl substituent, invariably increased antiviral activities. However, optimal antiviral activities were manifested by compounds where both meta groups in the arylsulfonyl moiety were substituted and one of the substituents was a methyl group. Such a disubstitution led to compounds 3v, 3w, 3x, and 3y having IC50 values against HIV-1 in the low nanomolar range. When gauged for their broad-spectrum antiviral activity against key non-nucleoside reverse transcriptase inhibitor (NNRTI) related mutants, all the di-meta-substituted sulfones 3u-z and the 2-naphthyl analogue 3ee generally showed single-digit nanomolar activity against the V106A and P236L strains and submicromolar to low nanomolar activity against strains E138K, V108I, and Y188C. However, they showed a lack of activity against the K103N and Y181C mutant viruses. The elucidation of the X-ray crystal structure of the complex of 3v (739W94) in HIV-1 reverse transcriptase showed an overlap in the binding domain when compared with the complex of nevirapine in HIV-1 reverse transcriptase. The X-ray structure allowed for the rationalization of SAR data and potencies of the compounds against the mutants.

Retinal detachment and degeneration in response to subretinal perfluorodecalin in rabbit eyes

Perfluorocarbon liquids, including perfluorodecalin (PFD), are useful intraoperative tools in complicated vitreoretinal surgery, such as for giant retinal tears, PVR and intraocular foreign bodies. Due to its high specific gravity (1.91 g/cm3) subretinal complications of PFD may occur. The consequences of subretinal PFD were studied in 23 albino rabbits (28 eyes). Using glass micropipettes (outer diameter of tip 100-120 microns), we injected 50-100 microliters PFD subretinally via the vitreous space. The same volume of BSS was injected into 18 control eyes. Eyes were monitored by indirect ophthalmoscopy and examined by light and electron microscopy at 1, 2 and 3 days, and 1, 2, 4 and 12 weeks. Progressive retinal detachments with newly formed retinal breaks in the inferior quadrants developed in 26 of 28 eyes. As early as 1 day postoperatively, subretinal PFD induced loss of outer and inner segments. Local retinal necrosis occurred in 4 eyes 5-7 days after surgery. A marked vacuole formation in retinal layers and PFD emulsification were regularly seen. The control eyes healed spontaneously. Toxic, mechanical and barrier effects may have caused the retinal damage. We advocate that all PFD be removed from the eye at surgery.

First intracellular loop of the human cholecystokinin-A receptor is essential for cyclic AMP signaling in transfected HEK-293 cells

Cholecystokinin (CCK)-A and CCK-B receptors are highly homologous members of the seven transmembrane domain G-protein-coupled receptor superfamily. Genes of both receptors contain five exons and share a similar exon-intron organization. To determine the structural basis of CCK-A receptor (CCK-AR) functionally coupled to Gs, a series of chimeric mutants were constructed by replacing exons of human CCK-B receptor (CCK-BR), from the second to the fifth (last) exon, with human CCK-AR counterparts. Binding and signal transduction properties of wild-type and chimeric receptors were examined in stably transfected HEK-293 cells. Chimeric receptors that maintained high affinity binding to CCK exhibited dose-dependent increases in intracellular calcium mobilization similar to both wild-type receptors. However, only the wild-type CCK-AR and chimeric mutants containing the second exon of CCK-AR were able to mediate significantly greater increases in intracellular cAMP content and adenylyl cyclase activity compared with wild-type CCK-BR. A CCK-BR mutant was further constructed by replacing five amino acids, Gly-Leu-Ser-Arg-(Arg)-Leu, in the first intracellular loop with the corresponding five CCK-AR specific amino acids, Ile-Arg-Asn-Lys-(Arg)-Met. The resultant receptor maintained high affinity binding to both CCK and gastrin and dose-dependent calcium responses similar to wild-type CCK-BR. However, this first intracellular loop mutant also gained positive cAMP responses to both sulfated CCK-8 and gastrin-17 with EC50 values of 8.5 +/- 1 nM and 23 +/- 7 nM, respectively. These data suggest that the first intracellular loop of CCK-AR is essential for coupling to Gs and activation of adenylyl cyclase signal transduction cascade.

Sensitive and universal indirect chemiluminescence detection for capillary electrophoresis of cations using cobalt(II) as a probe ion

Highly sensitive and universal indirect chemiluminescence detection for capillary electrophoresis of cations was described. This novel method is based on use of the ultrasensitive cobalt(II) as a probe ion in the running buffer. A strong and stable background chemiluminescent signal can be generated by the luminol-hydrogen peroxide reaction catalyzed by cobalt(II) ion. Displacement of the cobalt(II) probe ion in the running buffer by a migrating sample cation results in a quantifiable decrease in the background signal. The conditions for electrophoresis and the chemiluminescent reaction were systematically investigated using a commercial capillary electrophoresis instrument with an in-house-built chemiluminescence detector. Under the optimal conditions, the detection limits of the concentration for manganese(II), cadmium(II), nickel(II), lead(II), and 14 lanthanides were (3.0-6.0) x 10(-9) mol/L (S/N = 3), which was approximately 3 orders of magnitude better than indirect UV detection and 2 orders better than indirect laser-induced fluorescent detection. A mixture of 18 metal ions including 14 lanthanides was efficiently separated within 3.5 min using lactate to partially complex the metal ions. Our data demonstrated that CE with indirect CL detection was a powerful and universal tool for analysis of inorganic and organic cations.

Identifying transmembrane states and defining the membrane insertion boundaries of hydrophobic helices in membrane-inserted diphtheria toxin T domain

The membrane topography of proteins that convert between soluble and membrane-inserted states has proven a challenging problem. In particular, it has been difficult to define both whether a transmembrane orientation is achieved and what are the boundaries of membrane-inserted segments. In this report the fluorescence of bimane-labeled Cys residues and the binding of anti-BODIPY antibodies to BODIPY-labeled Cys residues are combined to define these features for helices TH8 and TH9 of the T domain of diphtheria toxin. Using a series of labeled residues the topography of these helices was examined in both conformations of membrane-inserted T domain identified previously (Wang, Y., Malenbaum, S. E., Kachel, K., Zhan, H., Collier, R. J., and London, E. (1997) J. Biol. Chem. 272, 25091-25098). In the shallowly inserted conformation these helices are found to be aligned close to the cis surface of the bilayer all along their sequences. In contrast, in the more deeply inserted conformation most TH8 and TH9 residues examined located in a non-polar environment, with the boundaries of the membrane-inserted sequences close to residues 324 and 372-374 on the cis (insertion) side of the bilayer. It was also found that residues 348 and 349, which are in the loop connecting TH8 and TH9, reached the opposite trans side of the bilayer, but did not protrude fully into the aqueous environment. These boundaries suggest the membrane-inserted segments of TH8 and TH9 form transmembrane helices about 25 residues in length, and suggest that they are connected by a tight turn. It is concluded that this combination of fluorescent techniques can be combined to obtain transmembrane helix topography.

Altered cardiac excitation-contraction coupling in ventricular myocytes from spontaneously diabetic BB rats

Cardiac excitation-contraction (E-C) coupling abnormalities in chemically induced diabetes have been well defined. Heart dysfunction has also been reported in diabetes of genetic origin. The purpose of this study was to determine whether heart dysfunction in genetically predisposed diabetes is attributable to impaired E-C coupling at the cellular level. Myocytes were isolated from 1-yr-old BioBreed (BB) spontaneously diabetic-prone (BB/DP) rats and their diabetic-resistant littermates (BB/DR). Mechanical properties were evaluated by use of a video edge-detection system. Myocytes were electrically stimulated at 0.5 Hz. The contractile properties analyzed included peak shortening (PS), time-to-peak shortening (TPS), time-to-90% relengthening (TR(90)), and maximal velocities of shortening and relengthening (+/-dL/dt). Intracellular Ca(2+) handling was evaluated with fura 2 fluorescent dye. Myocytes from spontaneously diabetic hearts exhibited a depressed PS, prolonged TPS and TR(90), and reduced +/-dL/dt. Consistent with the mechanical response, myocytes from the BB/DP group displayed reduced resting and peak intracellular Ca(2+) concentration associated with a slowed Ca(2+)-transient decay. Furthermore, myocytes from BB/DP hearts were less responsive to increases in extracellular Ca(2+) and norepinephrine and equally responsive to increases in stimulation frequency and KCl compared with those from the BB/DR group. These results suggest that the genetic diabetic state produces altered cardiac E-C coupling, in part, because of abnormalities of the myocyte, similar to that demonstrable after chemically induced diabetes or during human diabetes.

A 6-bp deletion in the TYRP1 gene causes the brown colouration phenotype in Chinese indigenous pigs

Brown coat colour has been described in Chinese-Tibetan, Kele, and Dahe pigs. Here, we report the identification of a causal mutation underlying the brown colouration. We performed a genome-wide association study (GWAS) on Tibetan and Kele pigs, and found that brown colours in Chinese breeds are controlled by a single locus on pig chromosome 1. By using a haplotype-sharing analysis, we refined the critical region to a 1.5-Mb interval that encompasses only one pigmentation gene: tyrosinase-related protein 1 (TYRP1). Mutation screens of sequence variants in the coding region of TYRP1 revealed a strong candidate causative mutation (c.1484_1489del). The protein-altering deletion showed complete association with the brown colouration across Chinese-Tibetan, Kele, and Dahe breeds by occurring exclusively in brown pigs (n=121) and lacking in all non-brown-coated pigs (n=745) from 27 different breeds. The findings provide the compelling evidence that brown colours in Chinese indigenous pigs are caused by the same ancestral mutation in TYRP1. To our knowledge, this study gives the first description of GWAS identifying causal mutation for a monogenic trait in the domestic pig.

Upper esophageal sphincter function during gastroesophageal reflux events revisited

Upper esophageal sphincter (UES) function during gastroesophageal reflux events is not completely elucidated because previous studies addressing this issue yielded conflicting results. We reexamined the UES pressure response to intraluminal esophageal pressure and pH changes induced by reflux events. We studied 14 healthy, asymptomatic volunteers (age 49 +/- 6 yr) and 7 gastroesophageal reflux disease patients (age 48 +/- 5 yr). UES pressure, intraesophageal pressure, and pH were monitored at the distal, middle, and proximal esophagus concurrently in the supine position 1 h before and 2 h after a 1,000-calorie meal. A total of 321 reflux events were identified by the development of abrupt reflux-induced intraesophageal pressure increase (IPI); 285 events occurred in patients and 36 in control subjects. In control subjects 33 of 36 and in patients 252 of 285 IPI events were associated with a pH drop. Among patients and control subjects, 99% and 100%, respectively, of all IPI events irrespective of pH drop were associated with abrupt increase in UES pressure (34 +/- 2 and 27 +/- 6 mmHg, respectively). The average percentage of maximum UES pressure increase over prereflux values ranged between 66% and 96% (control subjects) and 34% and 122% (patients). IPIs induced by both acidic and nonacidic reflux events evoke strong UES contractile responses.

Sensing with Exceptional Surfaces in Order to Combine Sensitivity with Robustness

Exceptional points (EPs) are singularities that arise in non-Hermitian physics. Current research efforts focus only on systems supporting isolated EPs characterized by increased sensitivity to external perturbations, which makes them potential candidates for building next generation optical sensors. On the downside, this feature is also the Achilles heel of these devices: they are very sensitive to fabrication errors and experimental uncertainties. To overcome this problem, we introduce a new design concept for implementing photonic EPs that combine the robustness required for practical use together with their hallmark sensitivity. Particularly, our proposed structure exhibits a hypersurface of Jordan EPs embedded in a larger space, and having the following peculiar features: (1) A large class of undesired perturbations shift the operating point along the exceptional surface (ES), thus, leaving the system at another EP which explains the robustness; (2) Perturbations due to back reflection or backscattering force the operating point out of the ES, leading to enhanced sensitivity. Importantly, our proposed geometry is relatively easy to implement using standard photonics components and the design concept can be extended to other physical platforms such as microwave or acoustics.

Histamine H3 receptor-mediated suppression of inhibitory synaptic transmission in the submucous plexus of guinea-pig small intestine

Conventional intracellular microelectrodes and marker injection techniques were used to study the actions of histamine on inhibitory synaptic transmission in the submucous plexus of guinea-pig small intestine. Bath application of histamine (1-300 microM) reversibly suppressed both noradrenergic and non-adrenergic slow inhibitory postsynaptic potentials in a concentration-dependent manner. These effects of histamine were mimicked by the selective histamine H(3) receptor agonist R(-)-alpha-methylhistamine but not the selective histamine H(1) receptor agonist, 6-[2-(4-imidazolyl)ethylamino]-N-(4-trifluoromethylphenyl) heptanecarboxamide (HTMT dimaleate), or the selective histamine H(2) receptor agonist, dimaprit. The histamine H(3) receptor antagonist, thioperamide, blocked the effects of histamine. Histamine H(1) and H(2) receptor antagonists did not change the action of histamine. Hyperpolarizing responses to focal application of norepinephrine or somatostatin by pressure ejection from micropipettes were unaffected by histamine and R(-)-alpha-methylhistamine. The results suggest that histamine acts at presynaptic histamine H(3) receptors on the terminals of sympathetic postganglionic fibers and intrinsic somatostatinergic nerves in the small intestine to suppress the release of the inhibitory neurotransmitters, norepinephrine and somatostatin.

Continuous and discontinuous changes in the unit cell of HIV-1 reverse transcriptase crystals on dehydration

A crystal form of HIV-1 reverse transcriptase (RT) complexed with inhibitors showed diffraction to a high-resolution limit of 3.7 A. Instability in the unit-cell dimensions of these crystals was observed during soaking experiments, but the range of this variability and consequent change in lattice order was revealed by a chance observation of dehydration. Deliberately induced dehydration results in crystals having a variety of unit cells, the best-ordered of which show diffraction to a minimum Bragg spacing of 2.2 A. In order to understand the molecular basis for this phenomenon, the initial observation of dehydration, the data sets from dehydrated crystals, the crystal packing and the domain conformation of RT are analysed in detail here. This analysis reveals that the crystals undergo remarkable changes following a variety of possible dehydration pathways: some changes occur gradually whilst others are abrupt and require significant domain rearrangements. Comparison of domain arrangements in different crystal forms gives insight into the flexibility of RT which, in turn, may reflect the internal motions allowing this therapeutically important enzyme to fulfill its biological function.

Analysis of single-strand conformation polymorphism by capillary electrophoresis with laser-induced fluorescence detection using short-chain polyacrylamide as sieving medium

A rapid analysis of single-strand conformation polymorphism (SSCP) by capillary electrophoresis with laser-induced fluorescence (CE-LIF) detector was developed using a short-chain, linear polyacrylamide (PA) as sieving medium. Capillary filling of this low-viscosity medium and medium replacement were carried out by commercial capillary electrophoresis instruments. The approach was successfully applied to detect the C677T mutation of methylenetetrahydrofolate reductase gene. The influences of factors such as the concentration of polymers, voltage, temperature, and additives on the SSCP analysis were systematically investigated. Using 6% PA sieving medium and high electric field, four strands were resolved within 11 min in a DNA sample heterozygous for the C677T mutation, and a characteristic pattern was apparent for each of the three genotypes. When using multiple injection mode, the average analysis time per sample was reduced to about 4 min. In conclusion, our results indicate that CE-LIF may be an alternative to conventional SSCP analysis based on slab gel electrophoresis for the detection of genetic mutations. The technique is simple and rapid and is well suited to analysis of large numbers of clinical samples.

North Pacific freshwater events linked to changes in glacial ocean circulation

There is compelling evidence that episodic deposition of large volumes of freshwater into the oceans strongly influenced global ocean circulation and climate variability during glacial periods^1,2. In the North Atlantic region, episodes of massive freshwater discharge to the North Atlantic Ocean were related to distinct cold periods known as Heinrich Stadials^1-3. By contrast, the freshwater history of the North Pacific region remains unclear, giving rise to persistent debates about the existence and possible magnitude of climate links between the North Pacific and North Atlantic oceans during Heinrich Stadials^4,5. Here we find that there was a strong connection between changes in North Atlantic circulation during Heinrich Stadials and injections of freshwater from the North American Cordilleran Ice Sheet to the northeastern North Pacific. Our record of diatom δ¹⁸O (a measure of the ratio of the stable oxygen isotopes ¹⁸O and ¹⁶O) over the past 50,000 years shows a decrease in surface seawater δ¹⁸O of two to three per thousand, corresponding to a decline in salinity of roughly two to four practical salinity units. This coincided with enhanced deposition of ice-rafted debris and a slight cooling of the sea surface in the northeastern North Pacific during Heinrich Stadials 1 and 4, but not during Heinrich Stadial 3. Furthermore, results from our isotope-enabled model⁶ suggest that warming of the eastern Equatorial Pacific during Heinrich Stadials was crucial for transmitting the North Atlantic signal to the northeastern North Pacific, where the associated subsurface warming resulted in a discernible freshwater discharge from the Cordilleran Ice Sheet during Heinrich Stadials 1 and 4. However, enhanced background cooling across the northern high latitudes during Heinrich Stadial 3-the coldest period in the past 50,000 years⁷-prevented subsurface warming of the northeastern North Pacific and thus increased freshwater discharge from the Cordilleran Ice Sheet. In combination, our results show that nonlinear ocean-atmosphere background interactions played a complex role in the dynamics linking the freshwater discharge responses of the North Atlantic and North Pacific during glacial periods.