Reversible morphological changes of assembled supramolecular amphiphiles triggered by pH-modulated host-guest interactions.

Reversible template-directed micellar-size and shape modulation by virtue of host-guest reversible docking of molecular templates at the micellar-solvent interface was achieved in water. By combining a π-electron deficient bipyridinium-based gemini amphiphile which is capable of binding and aligning with a π-electron rich tri(ethylene glycol)-disubstituted 1,5-diaminonaphthalene, a switchable detergent system which operates through the pH-responsive formation of bisammonium dications was realised. The binding of the 1,5-diaminonaphthalene guest to the bipyridinium-based micellar aggregate superstructure can be actuated by the addition of acid and base. Upon the addition of acid, protonation of the guest forming the dication deactivates molecular recognition with the charged head groups of the micellar aggregate by Coulombic repulsion. This process is completely reversible upon the addition of base, whereby the guest reintercalates into the superstructure -again forming donor-acceptor π-π stacks at the micellar-solvent interface amongst contiguous surfactant head groups. Synchrotron small angle X-ray scattering and dynamic laser light scattering confirm that this form of reversible directionally-templated micellisation results in an oblate spheroid-to-lamellar micelle morphological transition with a stabilising net decrease in the free energy of micellisation of 1.4 kcal mol(-1) per hydrophobic tail.

Antarctic glaciation caused ocean circulation changes at the Eocene-Oligocene transition.

Two main hypotheses compete to explain global cooling and the abrupt growth of the Antarctic ice sheet across the Eocene-Oligocene transition about 34 million years ago: thermal isolation of Antarctica due to southern ocean gateway opening, and declining atmospheric CO2 (refs 5, 6). Increases in ocean thermal stratification and circulation in proxies across the Eocene-Oligocene transition have been interpreted as a unique signature of gateway opening, but at present both mechanisms remain possible. Here, using a coupled ocean-atmosphere model, we show that the rise of Antarctic glaciation, rather than altered palaeogeography, is best able to explain the observed oceanographic changes. We find that growth of the Antarctic ice sheet caused enhanced northward transport of Antarctic intermediate water and invigorated the formation of Antarctic bottom water, fundamentally reorganizing ocean circulation. Conversely, gateway openings had much less impact on ocean thermal stratification and circulation. Our results support available evidence that CO2 drawdown--not gateway opening--caused Antarctic ice sheet growth, and further show that these feedbacks in turn altered ocean circulation. The precise timing and rate of glaciation, and thus its impacts on ocean circulation, reflect the balance between potentially positive feedbacks (increases in sea ice extent and enhanced primary productivity) and negative feedbacks (stronger southward heat transport and localized high-latitude warming). The Antarctic ice sheet had a complex, dynamic role in ocean circulation and heat fluxes during its initiation, and these processes are likely to operate in the future.

The controlled fabrication of nanopores by focused electron-beam-induced etching.

The fabrication of nanometric holes within thin silicon-based membranes is of great importance for various nanotechnology applications. The preparation of such holes with accurate control over their size and shape is, thus, gaining a lot of interest. In this work we demonstrate the use of a focused electron-beam-induced etching (FEBIE) process as a promising tool for the fabrication of such nanopores in silicon nitride membranes and study the process parameters. The reduction of silicon nitride by the electron beam followed by chemical etching of the residual elemental silicon results in a linear dependence of pore diameter on electron beam exposure time, enabling accurate control of nanopore size in the range of 17-200 nm in diameter. An optimal pressure of 5.3 x 10(-6) Torr for the production of smaller pores with faster process rates, as a result of mass transport effects, was found. The pore formation process is also shown to be dependent on the details of the pulsed process cycle, which control the rate of the pore extension, and its minimal and maximal size. Our results suggest that the FEBIE process may play a key role in the fabrication of nanopores for future devices both in sensing and nano-electronics applications.

The sequences of genes bordering oriT in the enterotoxin plasmid P307: comparison with the sequences of plasmids F and R1.

The nucleotide sequences of the enterotoxin plasmid P307 transfer genes traM, finP, traJ, traY, and gene 19 were determined. Gene 19 is highly conserved; its product is very similar to that coded by the F and R1 plasmids. The TraM protein is similar in P307 and in F; the R1 sequence shows differences in the 40 N-terminal amino acids. The traJ product is very different in P307, F, and R1. The traY gene from P307, which in F is almost twice as long, is similar in size to that from R1. The finP RNA shows a high degree of homology with that from R1 and F, except for the two loop regions where base changes were observed. The genes coding for proteins, except traY, could be expressed in minicell- and T7 promoter-driven expression systems, whereas traJ and gene 19 could be expressed only in the latter system.

Efficacy of delayed administration of crotalid antivenom and crystalloid fluids.

Clinical and research reports suggest that the efficacy of antivenom declines when its administration is delayed after envenomation. A controlled sequential trial was performed comparing the efficacy of three treatments to untreated controls when applied 1 hr after subcutaneous injection of rats with Crotalus atrox venom. Survival was decreased in all groups when treatment was delayed for 1 hr. Survival was highest in animals treated with both antivenom and saline, followed by antivenom alone, saline alone and then untreated animals.

The origin of transfer of P307.

The DNA fragment carrying the oriT region from the enterotoxin plasmid P307 was isolated and its polynucleotide sequence was determined. Using Southern hybridization assays with a synthetic oligonucleotide probe, the oriT region was identified on a 7.9-kb EcoRI fragment from P307. By ligating the fragment with the cloning vector pUC119, plasmid pAG10 was obtained. The physical map of the insert was determined and oriT was located on a 540-bp BglII/SalI fragment. After this fragment was subcloned into sequencing phages, the polynucleotide sequence was established. Part of the sequence proved to be almost identical to segments of the oriT regions of the plasmids F and R1; another neighboring region was very different among all three sequences. The polynucleotide sequence proximal to traM is highly similar to that of F but different from that of R1.

Are urine dipsticks reliable indicators of hematuria in blunt trauma patients?

Dipstick results in patients with blunt trauma have not been demonstrated to be predictive of the amount of microscopic hematuria. Our study examined the relationship between dipstick results and the degree of microscopic hematuria in 185 patients admitted to our emergency department following blunt trauma. Urine samples of 169 were dipsticked; the remaining 16 were grossly bloody. A wide range of microscopic hematuria results was obtained for each dipstick value. Of the 80 patients with negative dipsticks, 15 (18.7%) actually had microscopic hematuria. Conversely in 16 of 32 patients (50%) with a "trace" positive dipstick value, no microscopic hematuria was present. Similarly the dipstick value of 1+ had three of 14 (21%) false positives. False positives were recorded seven of 26 times (27%) for 2+, and three of 17 times (18%) for 3+ dipstick readings. We conclude that dipstick results do not correlate well with the presence or absence of hematuria in patients with blunt trauma. Microscopic urinalysis is a better test on which to base the decision to perform further diagnostic tests in the evaluation of the urinary tract.

Oxalate and chloride absorption by the rabbit colon: sensitivity to metabolic and anion transport inhibitors.

The effects of transport inhibitors on the movements of oxalate and chloride across the isolated short circuited rabbit colon were studied. Net oxalate absorption was shown in this species and was shown to be an energy dependent process as indicated by its sensitivity to 2-4 dinitrophenol (DNP) 10(-4)M. Mucosal addition of 4-acetamido-4-isothiocyano-2,-stilbene-2,2'-disulfonic acid (SITS) 10(-4)M abolished the net flux of both oxalate and chloride. Acetazolamide (8 mM) in bicarbonate free buffer significantly reduced the mucosal to serosal flux of both anions. These results suggest that in rabbit colon, oxalate and chloride share a common transport pathway and implicate the chloride bicarbonate exchange system. This study also confirms that chloride absorption by the short circuited rabbit colon is an electrically silent process and presents evidence that suggests that chloride absorption is mediated by a chloride bicarbonate exchange system located in the apical membrane of absorbing colonic epithelial cells.

Role of tight-junctional pathways in bile salt-induced increases in colonic permeability.

The effects of a dihydroxy bile salt, taurochenodeoxycholate (TCDC), on the permeability and conductance of isolated, short-circuited segments of the rabbit descending colon were examined using conventional Ussing chamber techniques. Increasing concentrations of TCDC (1-4 mM) produced dose-dependent increases in sodium backflux (JNas leads to m) and tissue conductance (Gt) when applied to either the mucosal or serosal salines. However, mucosal addition was twice as potent in increasing JNas leads to m and Gt at 4 mM. Tracer experiments indicated that the transepithelial serosal-to-mucosal fluxes of sodium and mannitol are via an aqueous, unrestricted, free-solution pathway, while albumin movements are restricted through this pathway both in the absence and presence of mucosal TCDC. The changes in JNas leads to m, JMans leads to m, and Gt caused by 4 mM mucosal TCDC were largely reversed by rinsing the mucosal chamber with fresh buffer. It was also observed that osmotically induced volume flows in the serosal-to-mucosal direction could offset or reverse the changes in Gt produced by 2 mM mucosal TCDC, suggesting that the enhanced conductance pathway is in series with the lateral intercellular spaces. Taken together, these results suggest that low concentrations of TCDC alter the integrity of tight-junctional complexes between the epithelial cells of the rabbit colon.

Dihydroxy bile salt-induced alterations in NaCl transport across the rabbit colon.

The effects of increasing mucosal or serosal concentrations (1-4 mM) of taurochenodeoxycholate (TCDC) on sodium chloride transport across the isolated, short-circuited rabbit colon were examined. Mucosal TCDC produced dose-related increases in tissue conductance (Gt) and the unidirectional fluxes of Na+ and Cl- and dose-related decreases in net NaCl absorption. At 4 mM mucosal TCDC, Gt was increased fivefold, net sodium flux (JNanet) was reduced 50%, and JClnet was abolished. Serosal TCDC also produced dose-dependent changes in permeability that were quantitatively different. Four millimolar serosal TCDC produced a 2.7-fold increase in Gt, abolished JNanet, and stimulated electrogenic Cl- secretion. TCDC-induced Cl- secretion was stimulated by 10(-5) M serosal TCDC, inhibited by serosal furosemide or ouabain, did not alter theophylline-induced secretion (and vice versa), and occurred in the absence of serosal Ca2+. It is suggested that 1) TCDC inhibition of sodium absorption is indirect (i.e., not simply due to a reduction in the activity of the Na "pump," since Cl- secretion persists during conditions that abolish JNanet) and 2) TCDC induces Cl- secretion by enhancing the activity of basolateral membrane adenylate cyclase.

Vanadium ion stimulation of chloride secretion by rabbit colonic epithelium.

Ionized forms of vanadium are known to exert diverse biological activities. Of particular interest in the inhibitory action of the vanadium ion on (Na+ + K+)-ATPase. This report describes another action of the vanadium ion on the rabbit colonic epithelium. Micromolar quantities of vanadate, applied to the serosal side of the isolated rabbit colonic epithelium, result in a stimulation of electrogenic chloride secretion by this epithelium. Sodium transport is unaffected by the vanadium ion in the concentrations used in this study. It is proposed that the vanadyl ion activates adenylate cyclase and thereby initiates subsequent secretory events.

Sodium-coupled nonelectrolyte transport across epithelia: emerging concepts and directions.

Since the proposal of the sodium-gradient hypothesis, research efforts have focused on two major areas: 1) establishing the thermodynamic efficacy of the electrochemical gradient for sodium as a driving force for uphill solute accumulation, and 2) determining the mechanism of energy coupling in cotransport systems. On the whole it is now reasonably well established that the Na+ electrochemical gradient can indeed energize the uphill accumulation of various nonelectrolytes in epithelia. This conclusion is substantiated by electrophysiological studies on intact epithelia using both conventional and Na+-selective microelectrodes and has been repeatedly verified in studies using brush-border membrane vesicles. One important additional concept that has emerged from these studies is that the overall transport process is intimately associated with, and perhaps controlled by, the electrical properties of leaky epithelia. The mechanism of energy coupling, as deduced from kinetic studies and modeling, has proven to be more elusive. Interpretations of earlier kinetic measurements on intact epithelia are complicated by unstirred layer effects and varying electrochemical Na+ gradients. Even more recent studies using brush-border membrane vesicles have failed to provide a unified mechanism, even for Na+-glucose transport, because of the various methods used to extract kinetic parameters and the variety of assumptions underlying different kinetic models. The common assumption that a translocation step rate limits the coupled entry process has been recently challenged, leading to novel proposals that are not based on mobile carriers. Future mechanistic studies will undoubtedly rely on recent advances in the isolation and purification of Na+-dependent proteins and their subsequent reconstitution into well-defined artificial membranes.

Oxalate transport across the isolated rat colon. A re-examination.

A net absorption of oxalate and chloride was observed when isolated, short-circuited segments of rat colon were bathed by a calcium-containing buffer. Removal of calcium promoted a two-fold decrease in transmural resistance, while the net chloride flux was reduced and the net oxalate transport abolished. It was concluded that net oxalate absorption was not observed in previous studies (employing calcium-free buffers) because calcium is reqiured to maintain the integrity of the conductive pathways across colonic epithelia.

Calcium transport across avian uterus. III. Comparison of laying and nonlaying birds.

Transepithelial calcium fluxes were measured across isolated uterus of laying, nonlaying, and molting quail under conditions where no electrochemical difference existed across the tissue. Net uterine transfer of calcium in molting and nonlaying birds occurs in the secretory direction and is approximately one-fifth the value obtained for laying birds. The carbonic anhydrase enzyme activity of uteri from laying birds is twice that of uteri from molting birds and five times greater than that of uteri from nonlaying birds. When measured in the presence and absence of 2-mercaptoethanol or dithiothreitol, no statistical difference exists in uterine carbonic anhydrase activities of laying birds or the inhibitory effect of acetazolamide. These results indicate that nonlaying and molting quail secrete calcium at a rate much lower than that of laying quail and that net uterine transfer of calcium exhibits varing degrees of dependence on bicarbonate ion in laying, nonlaying, and molting birds. Carbonic anhydrase data sugges that the activtiy of this enzyme in the quail uterus may be related to uterine calcium secretion.