Factors influencing regional patency and configuration of the human infant upper airway

To study factors influencing patency and configuration of the upper airway, we studied 11 infant cadavers using endoscopy and photography. In most cases, studies were performed shortly after death. The naso-, oro-, and hypopharynx and the larynx were studied. The upper airway was sealed at the nose and mouth so that transmural airway pressure could be raised or lowered. As pressure was lowered airway closure was seen in each of the four regions studied. With respect to closing pressure, the oropharynx was the most compliant region and the larynx the least compliant. In the naso-, oro-, and hypopharynx, lowering the transmural pressure was associated with inward movement of the anterior, posterior, and lateral airway walls. In the larynx, closure occurred by vocal cord opposition in the midline. Tension applied to the genioglossus and geniohyoid tongue muscles had an effect opposite to that of airway suction, causing a more or less symmetrical dilation of the naso- and oropharynx. When the airway was closed, additional tension was needed to produce airway reopening, suggesting that adhesion forces act to maintain airway closure. Neck flexion caused pharyngeal closure, and neck extension caused pharyngeal dilation. Secretions adherent to the walls of the airway visibly narrowed its lumen. The relevance of these findings for the obstructive sleep apnea and laryngomalacia syndromes is discussed.     

Assessment of pharyngeal airway stability in normal and micrognathic infants

A current hypothesis for obstructive sleep apnea states that 1) negative airway pressure during inspiration can collapse the pharyngeal airway, and 2) neural control of pharyngeal airway-dilating muscles is important in preventing this collapse. To test this hypothesis we performed nasal mask occlusions to increase negative pharyngeal airway pressures during inspiration in eight normal and five micrognathic infants. Both groups developed midinspiratory pharyngeal obstruction, but obstruction was more frequent in micrognathic infants and varied in some infants with sleep state. The airway usually reopened with the subsequent expiration. The occasional failure to reopen was presumably due to pharyngeal wall adhesion. If airway obstruction occurred in sequential breaths during multiple-breath nasal mask occlusions in normal infants, there was a breath-by-breath change in the airway pressure associated with airway closure (airway closing pressure); the airway closing pressure became progressively more negative. Micrognathic infants showed less ability to improve the airway closing pressure, but this ability increased with age. These findings suggest that nasal mask occlusion can test the competence of the neuromuscular mechanisms that maintain pharyngeal airway patency in infants. Micrognathic infants had spontaneous midinspiratory pharyngeal airway obstructions during snoring. Their episodes of obstructive apnea began with midinspiratory pharyngeal obstruction similar to that seen during snoring and nasal mask occlusions. These findings imply a similar pathophysiology for snoring, spontaneous airway obstruction, and obstruction during snoring.     

Rapid transfer of DNA from agarose gels to nylon membranes.

The unique properties of nylon membranes allow for dramatic improvement in the capillary transfer of DNA restriction fragments from agarose gels (Southern blotting). By using 0.4 M NaOH as the transfer solvent following a short pre-treatment of the gel in acid, DNA is depurinated during transfer. Fragments of all sizes are eluted and retained quantitatively by the membrane; furthermore, the alkaline solvent induces covalent fixation of DNA to the membrane. The saving in time and materials afforded by this simple modification is accompanied by a marked improvement in resolution and a ten-fold increase in sensitivity of subsequent hybridization analyses. In addition, we have found that nylon membrane completely retains native (and denatured) DNA in transfer solvents of low ionic strength (including distilled water), although quantitative elution of DNA from the gel is limited to fragments smaller than 4 Kb. This property can be utilized in the direct electrophoretic transfer of native restriction fragments from polyacrylamide gels. Exposure of DNA to ultraviolet light, either in the gel or following transfer to nylon membrane, reduces its ability to hybridize.     

The stereochemical course of phospho transfer catalyzed by adenylosuccinate synthetase. A reaction pathway via a phosphorylated intermediate with net inversion

The stereochemical course of phospho transfer in the reaction catalyzed by adenylosuccinate synthetase from rat muscle has been determined with chiral [gamma-17O,18O]GTP gamma S as a substrate. The stereochemical configuration of the product, inorganic thiophosphate, was determined by 31P NMR after the compound was stereospecifically incorporated into ATP beta S. The reaction goes with net inversion of configuration, which is the course for a single phospho transfer, even though 6-phospho-IMP is probably an intermediate on the normal reaction pathway (Liebermann, I. (1956) J. Biol. Chem. 223, 327-339). The breakdown of this intermediate goes by C-O bond cleavage and so is not a true phospho transfer step. Thus, inversion of configuration during the course of this ligase reaction is consistent with a single phospho transfer step in the overall reaction, the formation of the phosphorylated intermediate.     

Transient breakdown in the selective permeability of the plasma membrane ofChlorella emersonii in response to hyperosmotic shock: Implications for cell water relations and osmotic adjustment

Summary In osmotic experiments involving cells of the euryhaline unicellular green algaChlorella emersonii exposed to hyperosmotic stress by immersion in a range of low molecular weight organic and inorganic solutes, a temporary breakdown in the selective permeability of the plasma membrane was observed during the initial phase of transfer to media of high osmotic strength (up to 2000 mosmol kg^–1). Thus, although the cells appeared to obey the Boyle-van't Hoff relationship in all cases, showing approximately linear changes in volume (at high salinity) as a function of the reciprocal of the external osmotic pressure, the extent of change was least for the triitols, propylene glycol and glycerol, intermediate for glucose, sorbitol, NaCl and KCl, with greatest changes in media containing the disaccharides sucrose and maltose. In NaCl-treated cells, uptake of external solute and loss of internal ions was observed in response to hyperosmotic treatment while sucrose-treated cells showed no significant uptake of external solute, although loss of intracellular K⁺ was observed. These observations suggest that the widely used technique of estimating cellular turgor, and osmotic/nonosmotic volume by means of the changes in volume that occur upon transfer to media containing increasing amounts of either a low molecular weight organic solute or an inorganic salt may be subject to error. The assumption that all algal cells behave as ideal osmometers, with outer membranes that are permeable to water but not to solutes, during the course of such experiments is therefore incorrect, and the data need to be adjusted to take account of hyperosmotically induced external solute penetration and/or loss of intracellular osmotica before meaningful estimates of cell turgor and osmotic volume can be obtained.     

A role for exon sequences and splice-site proximity in splice-site selection

Analysis of the in vitro splicing products of RNA precursors containing tandem duplications of the 5' or 3' splice sites of human beta-globin IVS 1 revealed that exon sequences play an important role in the relative use of the duplicated sites. These studies also show that the proximity of the 5' and 3' splice sites is an important determinant in the selection of splice-sites. Deletion, substitution, or even subtle changes of exon sequences can alter the pattern of splice-site selection, and in many cases the splice site adjacent to the altered exon is not used. The relative use of the duplicated splice sites can also be altered by diluting the splicing extract, suggesting that factors involved in splice-site selection are limiting.     

An electron paramagnetic resonance study of bovine alpha-lactalbumin-metal ion complexes

alpha-lactalbumin has at least three distinct cation binding regions: a Ca(II)-Gd(III) site, a Cu(II)-Zn(II) site and a VO2+ site as observed from electron paramagnetic resonance (EPR) studies of complexes with the bovine protein. Gadolinium, which bound to the calcium site of the protein with a subnanomolar dissociation constant, yielded EPR spectra at 9.5 GHz (X-band) that exhibited features from g = 8 to g = 2. At 35 GHz (Q-band) the central fine structure transition (Ms = 1/2----Ms = -1/2) gave a well-defined powder pattern. The zero-field splitting was large, as reflected in the second-order splitting of the central fine structure transition of about 1 kG. There was also evidence for additional, low affinity binding site(s) for Gd(III). Addition of either Zn(II) or Al(III) did not affect the amplitudes or positions of the bound Gd(III) EPR spectrum. The Cu(II)-alpha-lactalbumin complex gave a typical axially symmetric spectrum (g parallel = 2.260, g perpendicular = 2.056, A parallel = 171 G) with a partially resolved superhyperfine interaction attributable to at least one directly coordinated nitrogen ligand. Addition of Cu(II) to Gd(III)-alpha-lactalbumin gave an EPR spectrum that was a superposition of signals from the individual Gd(III)- and Cu(II)-alpha-LA spectra. The absence of any magnetic interactions in the Gd(III)-Cu(II)-alpha-lactalbumin species indicated that the two cation sites were more than 10 A apart. On the other hand, addition of Zn(II) to Cu(II)-alpha-lactalbumin gave a set of EPR lines due to free or loosely bound Cu(II), confirming that the Cu(II) was displaced by zinc.(ABSTRACT TRUNCATED AT 250 WORDS)     

Somatic embryogenesis from three commercially important inbreds of Zea mays

Zea mays (maize) genotypes B73, Mo17 and LH38 were evaluated for their capacity to undergo somatic embryogenesis. Over 1500 immature embryos (ie's) of B73, 2900 ie's of LH38 and 400 ie's of Mo17 were excised 10–17 days after pollination and plated on six different media. Overall response, reported as a percentage of the ie's plated that developed embryogenic callus, was 2.1%, 1.6% and 26% for LH38, B73 and Mo17, respectively. Best response on a given medium for each of these genotypes was 9.2% (LH38), 4.4% (B73) and 100% (Mo17). Other parameters examined for their effects on production of embryogenic callus included self vs. sib pollination, ear ranking (1st, 2nd or 3rd ear), and temperature shock, all of which had no significant effect. Plantlets regenerated from selected treatments of B73 have been grown to maturity, selfed or sibbed and seed collected for field evaluation.Abbreviations i.e. immature embryo - 2,4-D 2,4-di-chlorophenoxyacetic acid