The prone sleeping position impairs arousability in term infants.

OBJECTIVE: To investigate whether the prone sleeping position impaired arousal from sleep in healthy infants and whether this impairment was related to cardiorespiratory variables, temperature, or age. STUDY DESIGN: Healthy term infants (n = 24) were studied with daytime polysomnography on 3 occasions: 2 to 3 weeks after birth, 2 to 3 months after birth, and 5 to 6 months after birth. Multiple measurements of arousal threshold (cm H(2)O) in response to air-jet stimulation applied alternately to the nares were made in both active sleep and quiet sleep when infants slept both prone and supine. RESULTS: Arousal thresholds were significantly higher in both active sleep and quiet sleep when infants slept prone at 2 to 3 weeks and 2 to 3 months, but not at 5 to 6 months. These increases were independent of any sleep position-related change in either rectal or abdominal skin temperature, respiratory rate, oxygen saturation, or heart rate. CONCLUSIONS: The prone position significantly impairs arousal from both active sleep and quiet sleep in healthy term infants. This impairment in arousability occurred with no clinically significant changes in cardiorespiratory variables or body temperature. Decreased arousability from sleep in the prone position provides an important insight into its role as a risk factor for sudden infant death syndrome.

Interaction of a type II myosin with biological membranes studied by 2H solid state NMR.

Deuterium nuclear magnetic resonance spectroscopy (2H NMR) has been employed to investigate the interaction of lung type II myosin protein with neutral bilayers containing dimyristoylphosphatidylcholine (DMPC) as the only constituent and mixed bilayers containing the negatively charged lipid dimyristoylphosphatidylglycerol (DMPG). DMPC was deuterated at its headgroup by substituting the four protons at the alpha- and beta-positions (DMPC-d4) and the nine protons at the gamma-position (DMPC-d9). DMPG was perdeuterated at its headgroup (DMPG-d5). No changes were observed in the quadrupole splittings or spin-lattice relaxation times for the deuterated DMPC headgroup segments when increasing amounts of myosin were added to liposomes, made exclusively of DMPC-d9 or of DMPC-d4. However, upon the insertion of the negatively charged lipid DMPG at 1:1 molar ratio into the DMPC bilayers, myosin was found to interact electrostatically with the liposomes, thereby affecting significantly both the quadrupole splittings and spin-lattice relaxation rates of the alpha-, beta-, and gamma-deuterons in labeled DMPC. Monitoring DMPG-d5 in mixed DMPC/DMPG bilayers revealed a direct electrostatic interaction of DMPG with the protein, where positively charged lysine residues located at the tail domain of myosin provide the necessary sites for the interaction to occur. When ATP and Mg2+ were complexed to the head domain of myosin, a reduced interaction with the negatively charged bilayers was observed. The results clearly indicate that a type II myosin can interact with membranes without the need for a specific hydrophobic domain or an anchor in the protein molecule, provided that negatively charged lipids are present in the bilayer.

Spin label and 2H-NMR studies on the interaction of melanotropic peptides with lipid bilayers.

The interaction of the cationic tridecapeptide alpha-melanocyte stimulating hormone (alpha-MSH) and the biologically more active analog [Nle4, DPhe7]-alpha-MSH with lipid membranes was investigated by means of ESR of spin probes incorporated in the bilayer, and NMR of deuterated lipids. All spin labels used here, stearic acid and phospholipid derivatives labeled at the 5th and 12th position of the hydrocarbon chain, and the cholestane label, incorporated into anionic vesicles of DMPG (1,2-dimyristoyl-sn-glycero-3-phosphoglycerol) in the liquid-crystalline phase, indicated that both peptides decrease the motional freedom of the acyl chains. No peptide effect was detected with neutral lipid bilayers. Changes in the alpha-deuteron quadrupolar splittings and spin lattice relaxation time of DMPG deuterated at the glycerol headgroup paralleled the results obtained with ESR, showing that the peptides cause a better packing both at the headgroup and at the acyl chain bilayer regions. The stronger effect caused by the more potent analog in the membrane structure, when compared to the native hormone, is discussed in terms of its larger lipid association constant and/or its deeper penetration into the bilayer.