pH Dependence of Histidine Affinity for Blood-Brain Barrier Carrier Transport Systems for Neutral and Cationic Amino Acids

The effects of pH (3.5-7.5) on the brain uptake of histidine by the blood-brain barrier (BBB) carriers for neutral and cationic amino acids were tested, in competition with unlabeled histidine, arginine, or phenylalanine, with the single-pass carotid injection technique. Cationic amino acid ( [14C]arginine) uptake was increasingly inhibited by unlabeled histidine as the pH of the injection solution decreased. In contrast, the inhibitory effect of unlabeled histidine on neutral amino acid ( [14C]phenylalanine) uptake decreased with decreasing pH. Brain uptake indices with varying histidine concentrations indicated that the neutral form of histidine inhibited phenylalanine uptake whereas the cationic form competed with arginine uptake. Since phenylalanine decreased [14C]histidine uptake at all pH values whereas arginine did not, it was concluded that the cationic form of histidine had an affinity for the cationic carrier, but was not transported by it. We propose that the saturable entry of histidine into brain is, under normal physiological circumstances, mediated solely by the carrier for neutral amino acids.     

Use of phlorizin binding to demonstrate induction of intestinal glucose transporters

Summary We used specific binding of phlorizin to the intact intestinal mucosa in order to measure glucose transport site density in intestines of mice fed a high-carbohydrate or no-carbohydrate diet. Nonspecific binding varied with intestinal position but showed only modest dependence on diet. Specific binding to glucose transporters was 1.9 times greater in jejunum of high-carbohydrate mice than of no-carbohydrate mice; this ratio was the same as the ratio for V_max values of actived-glucose uptake between the two diet groups. The gradient in specific binding of phlorizin along the intestine paralleled the gradient in V_max of glucose transport. These results directly demonstrate that the increase in intestinal glucose transport caused by a high-carbohydrate diet is due to induction of glucose transporter. They also indicate that the normal positional graident in glucose transport along the intestine arises from a gradient in transporters, induced by the normal gradient in luminal glucose concentration.     

Contributions of unstirred-layer effects to apparent electrokinetic phenomena in the gall-bladder

Summary Passage of electric current across rabbit gall-bladder, which is preferentially permeable to cations, causes water flow towards the negative electrode, as expected for electroosmosis in a cation-selective membrane. Current passage also causes development of a polarization potential difference, i.e. a transepithelial potential difference (p.d.) which transiently remains after cessation of current flow and decays back to zero with a half-time of 22 to 90 sec. The polarization p.d. is due to current-induced local changes of salt concentration in unstirred layers, mainly at the serosal face of the epithelium. These changes originate through the so-called transport-number effect. Calculation shows that much of the observed current-induced water flow represents an osmotic flow due to these local concentration changes, rather than representing true electroosmosis. By implication, a large component of streaming potentials in the gall-bladder is a boundary diffusion potential, owing to water flow producing local changes of salt concentration in unstirred layers.     

The Mechanism of Isotonic Water Transport

The mechanism by which active solute transport causes water transport in isotonic proportions across epithelial membranes has been investigated. The principle of the experiments was to measure the osmolarity of the transported fluid when the osmolarity of the bathing solution was varied over an eightfold range by varying the NaCl concentration or by adding impermeant non-electrolytes. An in vitro preparation of rabbit gall bladder was suspended in moist oxygen without an outer bathing solution, and the pure transported fluid was collected as it dripped off the serosal surface. Under all conditions the transported fluid was found to approximate an NaCl solution isotonic to whatever bathing solution used. This finding means that the mechanism of isotonic water transport in the gall bladder is neither the double membrane effect nor co-diffusion but rather local osmosis. In other words, active NaCl transport maintains a locally high concentration of solute in some restricted space in the vicinity of the cell membrane, and water follows NaCl in response to this local osmotic gradient. An equation has been derived enabling one to calculate whether the passive water permeability of an organ is high enough to account for complete osmotic equilibration of actively transported solute. By application of this equation, water transport associated with active NaCl transport in the gall bladder cannot go through the channels for water flow under passive conditions, since these channels are grossly too impermeable. Furthermore, solute-linked water transport fails to produce the streaming potentials expected for water flow through these passive channels. Hence solute-linked water transport does not occur in the passive channels but instead involves special structures in the cell membrane, which remain to be identified.     

Sulfonates: novel electron acceptors in anaerobic respiration

The enrichment and isolation in pure culture of a bacterium, identified as a strain of Desulfovibrio, able to release and reduce the sulfur of isethionate (2-hydroxyethanesulfonate) and other sulfonates to support anaerobic respiratory growth, is described. The sulfonate moiety was the source of sulfur that served as the terminal electron acceptor, while the carbon skeleton of isethionate functioned as an accessory electron donor for the reduction of sulfite. Cysteate (alanine-3-sulfonate) and sulfoacetaldehyde (acetaldehyde-2-sulfonate) could also be used for anaerobic respiration, but many other sulfonates could not. A survey of known sulfate-reducing bacteria revealed that some, but not all, strains tested could utilize the sulfur of some sulfonates as terminal electron acceptor. Isethionate-grown cells of Desulfovibrio strain IC1 reduced sulfonate-sulfur in preference to that of sulfate; however, sulfate-grown cells reduced sulfate-sulfur in preference to that of sulfonate. Received: 2 May 1996 / Accepted: 8 June 1996     

Comparing Accuracy of Wrist Intra-articular Needle Placement Via Ulnocarpal Approach by Training Level: A Cadaveric Study

BackgroundIntra-articular injections are a standard therapy and diagnostic tool for a variety of wrist conditions. Accurate needle placement is crucial for proper therapeutic benefit and prevention of complications. While some studies claim accurate needle placement requires imaging, others conclude that anatomical guidance is sufficient. This study aimed to evaluate the accuracy of intra-articular wrist needle placement with the ulnocarpal approach across differing levels of training using clinical anatomy alone.MethodsFourteen fresh-frozen, above-elbow cadaveric specimens were used. Intra-articular needle placement into the wrist via an ulnocarpal approach was attempted by nine study participants: two interns, two junior-level residents, two senior-level residents, two hand fellows, and one attending hand surgeon. Each injection was performed based on clinical examination and landmarks alone. The number of attempts and total time taken for each injection was recorded.ResultsOverall success rate was 71%, (89 of 126 attempts) and did not vary significantly across levels of training. Average time for needle placement among all participants was 10.9 ± 6.5 seconds. Timing of successful intra-articular needle placement (10.4 ± 5.2 seconds) significantly differed between levels. However, timing did not trend in any direction with more or less training. No significant difference was noted in total attempts or attempts with successful outcomes when comparing level of training.ConclusionThe ulnocarpal approach is a viable option for injection or aspiration of the wrist without image guidance. We were unable to show any relevant trends with timing or number of attempts in comparison to level of training. Level of Evidence: V     

Quantification of microtubule stutters: dynamic instability behaviors that are strongly associated with catastrophe

Microtubules (MTs) are cytoskeletal fibers that undergo dynamic instability (DI), a remarkable process involving phases of growth and shortening separated by stochastic transitions called catastrophe and rescue. Dissecting DI mechanism(s) requires first characterizing and quantifying these dynamics, a subjective process that often ignores complexity in MT behavior. We present a Statistical Tool for Automated Dynamic Instability Analysis (STADIA) that identifies and quantifies not only growth and shortening, but also a category of intermediate behaviors that we term “stutters.” During stutters, the rate of MT length change tends to be smaller in magnitude than during typical growth or shortening phases. Quantifying stutters and other behaviors with STADIA demonstrates that stutters precede most catastrophes in our in vitro experiments and dimer-scale MT simulations, suggesting that stutters are mechanistically involved in catastrophes. Related to this idea, we show that the anticatastrophe factor CLASP2γ works by promoting the return of stuttering MTs to growth. STADIA enables more comprehensive and data-driven analysis of MT dynamics compared with previous methods. The treatment of stutters as distinct and quantifiable DI behaviors provides new opportunities for analyzing mechanisms of MT dynamics and their regulation by binding proteins.     

Genetic Screens Identify Host Factors for SARS-CoV-2 and Common Cold Coronaviruses

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