Na+ and K+ fluxes stimulated by Na+-coupled glucose transport: Evidence for a Ba2+-insensitive K+ efflux pathway in rabbit proximal tubules

Summary Addition of glucose or the nonmetabolizable analogue -methyl-d-glucoside to rabbit proximal tubules suspended in a glucoseand alanine-free buffer caused a sustained increase in intracellular Na⁺ content (+43±7 nmol · (mg protein)^–1) and a concomitant but larger decrease in K⁺ content (–72±11 nmol· (mg protein)^–1). A component of the net K⁺ efflux was Ba²⁺ insensitive, and was inhibited by high (1mm) but not low (10 m) concentrations of the diuretics, furosemide and bumetanide. The increase in intracellular Na⁺ content is consistent with the view that the increased rates of Na⁺ and water transport seen in the proximal tubule in the presence of glucose can be attributed (at least in part) to a stimulation of basolateral pump activity by an increased [Na⁺] _i .     

Modeling the kinetics of flavour release during drinking

Novel mathematical models for flavour release during drinking are described, based on the physiology of breathing and swallowing. Surprisingly, we conclude that most flavour molecules arriving in the nose are extracted from liquid left in the throat, after swallowing. The models are fit to real time flavour release data obtained using APCI-mass spectrometry. Before modelling, raw data are corrected for the effects of varying airflow rate, using the signal from acetone in exhaled air. A simple equilibrium batch extraction model correctly describes flavour release during the first breaths after swallowing a flavoured liquid. It shows that for eight volatiles, whose in vitro air-water partition coefficients vary by a factor of 500, the apparent in vivo air-saliva partition coefficients vary only by a factor of five. To interpret the kinetics of flavour release longer after swallowing, diffusion of flavour into the throat lining is included. This is done using a three-layer model for mass transfer in the throat. An analytical solution of this model gives good fits to typical data. These models de-couple the physiological and physico-chemical aspects of flavour release, clarifying the effect of behaviour on in-vivo flavour release.     

Single motherhood and mental health: implications for primary prevention

In this issue (page 639) Dr. Ellen L. Lipman and colleagues show that single motherhood is associated with an increased risk of affective disorder and poverty and with increased rates of mental health services utilization. These findings have important implications for primary prevention interventions that focus on the social determinants of family health. Studies have shown that higher levels of psychological distress among single mothers are more closely related to their exposure to stressors than to their personal vulnerability to stress. Research has also shown that the stresses that affect single-parent families are greater in degree but not in kind than those that affect other families. Therefore, intervention programs that address the needs of all families are preferable to those that target specific types of families. Community-based primary prevention programs can promote the well-being of all families by improving the social and economic conditions in which they live.     

13C-NMR measurements of muscle glycogen during low-intensity exercise

Glycogen metabolism in exercising gastrocnemius muscles was examined by natural abundance 13C nuclear magnetic resonance (NMR) spectroscopy. Five-minute 13C-NMR measurement of muscle glycogen had a reproducibility of +/- 6.5% (+/- 4.8 mM). Experiments were performed on healthy fed male and female subjects. Two protocols were followed. 1) Subjects performed plantar flexion from rest at 15, 20, or 25% of maximum voluntary contraction for up to 9 h. 2) Subjects predepleted gastrocnemius glycogen with heavy exercise and then either performed low-intensity exercise as before or rested. Gastrocnemius glycogen was measured by NMR at rest and after each hour of exercise. In some sessions, both the exercised leg and the nonexercised leg were monitored with 13C-NMR. In protocol 1, blood velocity in the femoral artery was similarly assessed with ultrasonography. During low-intensity exercise from rest (protocol 1) muscle glycogen fell to a new steady-state value after several hours and then remained constant despite continued exercise. Mean blood velocity increased ninefold within 2 min of onset of exercise and remained constant thereafter. After predepletion (protocol 2), muscle glycogen was repleted both during low-intensity exercise and at rest. After 1 h the amount of glycogen repletion was greater when coupled with light exercise [48.5 +/- 2.8 mM after 1 h of exercise, 39.7 +/- 1.1 mM after 1 h of rest (P less than 0.05)]. During subsequent light exercise, glycogen reached a steady-state value similar to that obtained in protocol 1, while in resting, recovery glycogen levels continued to increase (+2.7 mM/h) over a 7-h period.(ABSTRACT TRUNCATED AT 250 WORDS)     

Enhanced membrane permeabilization and antibacterial activity of a disulfide-dimerized magainin analogue

A cysteine substitution analogue of magainin-2 amide (magainin-F12W, N22C; denoted here as mag-N22C), and a disulfide-linked dimer prepared by air oxidation [(mag-N22C)(2)], were compared in their ability to release carboxyfluorescein (CF) from 100-nm large unilamellar vesicles (LUV) and to kill the Gram negative bacteria Stenotrophomonas maltophilia and Escherichia coli. The disulfide-dimerized peptide showed enhanced permeabilization and antimicrobial activity, when compared with the monomeric peptide, that was particularly marked at very low peptide concentrations. The enhanced CF-releasing activity of the dimer at low concentrations in vesicles results from (i) enhanced binding to negatively charged membrane surfaces and (ii) a low concentration dependence for permeabilization in the dimer compared to the monomer. The unique properties of the dimeric peptide suggest a role for structural diversity of antimicrobial peptides in frog skin, including the recent identification of a heterodimer composed of disulfide-linked amphipathic helical peptides [Batista et al. (2001) FEBS Lett. 494, 85-89]. Disulfide-dimerization of pore-forming, positively charged, amphipathic helical peptides may be a useful general approach to the generation of peptide antimicrobials having activity at very low concentrations.     

Ketamine/xylazine/butorphanol: a new anesthetic combination for rabbits.

Ketamine is often used in combination with tranquilizers to produce surgical anesthesia in rabbits. While generally effective, there is considerable variation in the depth and duration of anesthesia achieved with ketamine combinations. Butorphanol is a mixed agonist-antagonist opioid that is widely used in a variety of other species. In this study, the commonly used ketamine (35 mg/kg)/xylazine (5 mg/kg) combination is compared with ketamine (35 mg/kg)/xylazine (5 mg/kg)/butorphanol (0.1 mg/kg). Rabbits were anesthetized on consecutive weeks with one of the two regimens. Physiologic parameters including heart rate, respiratory rate, blood pressure and arterial blood gases (pH, PO2, PCO2) were measured throughout anesthesia. Loss of palpebral, pedal and righting reflexes were recorded and reflexes were subsequently evaluated. The addition of butorphanol prolonged reflex loss to 140% (X = 68 min +/- 20 SEM) of control for palpebral reflex; 506% (X = 52 min +/- 18 SEM) of control for pedal reflex; and 159% (X = 128 min +/- 21 SEM) of control for righting reflex. Addition of butorphanol to ketamine/xylazine resulted in mild alterations in the physiologic changes traditionally associated with this combination. Butorphanol can be safely added to the ketamine/xylazine combination in rabbits and results in moderate increases in the duration of reflex loss.     

pUb6060: a broad-host-range, DNA polymerase-I-independent ColE2-like plasmid

A ColE2-like, cryptic plasmid, pUB6060, of 5.8 kb has been found in a clinical isolate of Plesiomonas shigelloides. The complete sequence of pUB6060 has been determined and reveals a number of interesting features about the plasmid. The ColE2-like replication locus is linked to a functional ColE1-like mobilization locus. Replication is, unusually for ColE2 replicons, DNA polymerase-I-independent and may involve two, rather than the usual one, plasmid-encoded functions. Additionally, it carries two ORFs encoding products of unknown function. The pUB6060 replicon maintains a moderate plasmid copy number (10 per chromosome copy) and permits replication in diverse gram-negative bacteria.     

Comparative genomic hybridization detects secondary chromosomal deletions in Escherichia coli K-12 MG1655 mutants and highlights instability in the flhDC region

The use of whole-genome microarrays for monitoring mutagenized or otherwise engineered genetic derivatives is a potentially powerful tool for checking genomic integrity. Using comparative genomic hybridization of a number of unrelated, directed deletion mutants in Escherichia coli K-12 MG1655, we identified unintended secondary genomic deletions in the flhDC region in Δfnr, Δcrp, and ΔcreB mutants. These deletions were confirmed by PCR and phenotypic tests. Our findings show that nonmotile progeny are found in some MG1655 directed deletion mutants, and studies on the effects of gene knockouts should be viewed with caution when the mutants have not been screened for the presence of secondary deletions or confirmed by other methods.