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.     

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.     

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     

The effect of nerve growth factor on the development of sodium channels in PC12 cells

We have studied the development of the action potential Na+ channels in PC12 cells, an established line that has been useful as a model for neuronal differentiation. In continuous culture PC12 cells, although electrically inexcitable, nevertheless have a low level of Na+ channels as judged by the increase in 22Na+ uptake in the presence of veratridine and scorpion toxin. These two neurotoxins have been shown to promote activation of Na+ channels in a variety of electrically excitable cells. Following treatment with nerve growth factor (NGF), conditions which induce differentiation to an electrically excitably neuronal-cell type, the neurotoxin-activated 22Na+ uptake increases approximately 12-fold, on a per cell basis, reaching a maximum in 12-16 days. The dose-response curves for veratridine and scorpion toxin are unchanged by NGF treatment (K0.5 for veratridine, 18-14 microM; K0.5 for scorpion toxin, 120-96 nM). Na+ channels in both undifferentiated and differentiated cells are tetrodotoxin sensitive and NGF treatment has no effect on the inhibition constant (Ki, 10-12 nM). Na+ channel sites were measured directly by the specific binding of [3H]saxitoxin. In NGF-treated cells, the saxitoxin receptor density reaches 154 fmol/mg protein (Kd, 1.3 nM), a level comparable to other excitable cells. Levels in control cells were too low to measure accurately. These findings show that NGF treatment of PC12 cells leads to a substantial increase in the expression of neurotoxin-sensitive Na+ channels. Furthermore, these channels are pharmacologically similar, if not identical, to those which exist in undifferentiated cells and therefore do not appear to result from the conversion of preexisting channels.     

Isolation and elucidation of some functional properties of the "mute" catalytic subunit of cAMP-dependent protein kinase

A mute isoenzyme of type II cAMP-dependent protein kinase from rat muscle has been reported that is released from the regulatory subunit by cAMP but remains inactive until combination with heat- and acid-stable modulator has occurred. This enzyme has now been obtained in isolation free of the normal catalytic subunit using affinity chromatography with both an ATP analog (Blue Dextran/Sepharose) and a protein substrate analog (Kemptide/CH-Sepharose). Separation can be effected in both cases before activation of the mute enzyme. Affinity of the mute enzyme for Blue Dextran--a ligand specific for the dinucleotide fold in this kinase--is somewhat higher than that of the normal enzyme. Conversely, before reaction with the modulatory protein the mute enzyme will not bind at all to Kemptide/CH-Sepharose, where the normal enzyme elutes at 50 mM KCl. When pretreated with the modulatory protein and so activated, mute enzyme binds to Kemptide with a very high affinity and can only be eluted using a natural substrate (phosphorylase kinase), up to 500 mM salt being ineffective. The modulator thus appears to act through alteration of the protein substrate binding site on the enzyme.