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  • Cold exposure  (1)
  • Reaction-diffusion  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    European journal of applied physiology 73 (1996), S. 326-331 
    ISSN: 1439-6327
    Keywords: Posture ; Body temperature ; Cold exposure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We studied eight young adult men to see whether a supine posture caused a fall in body core temperature in the cold, as it does in thermoneutral conditions. In air at 31°C (thermoneutral), a supine posture for 3 h reduced mean aural, gastric, oesophageal and rectal temperatures by 0.2–0.4°C, compared to upright and increased femoral artery blood flow from 278 (SEM 42) ml · min−1 whilst upright to 437 (SEM 42) ml·min−1 whilst supine. In cold air (8°C) the supine posture failed to reduce these temperature differences significantly, or to increase femoral blood flow; it reduced heart rate, and increased arterial systolic and pulse pressures adjusted to carotid sinus level, less than in thermoneutral conditions. However, the behaviour of core temperature at the four sites was significantly nonuniform between the two postures in the cold, mainly because the supine posture tended to reduce rectal temperature. It may have done so by reducing heat production in the muscles of the pelvis, since it reduced overall metabolic rate from 105 (SEM 8) to 87 (SEM 4) W · m−2 in the cold. In other respects the results indicated that posture ceased to have an important effect on body core temperatures during cold stress.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1615-6102
    Keywords: Acetabularia acetabulum ; Whorl morphogenesis ; Reaction-diffusion ; EGTA ; Calcium receptors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The spacing between adjacent hairs in vegetative whorls ofAcetabularia acetabulum (formerlyA. mediterranea) was earlier reported as being quantitatively responsive to calcium ion concentration in the culture medium. We here report a quantitative response to the concentration of the calcium-chelator EGTA, in the opposite sense to the effect of calcium. (Increasing [Ca2+] diminishes the spacing; increasing [EGTA] increases it.) The earlier work was interpreted in terms of control of the spacing by a putative reaction-diffusion mechanism in the cell membrane, in which a receptor R was activated by calcium-binding to initiate the process. We extend this interpretation by treating CaEGTA as an uncompetitive inhibitor of the effect of calcium on R. This leads to thermodynamic constants for CaEGTA binding to the CaR complex: ΔH 298 0 =−250 ± 60 kJ/mol; ΔS 298 0 =−820 ± 200 J/mol · K. Consistency of the concentration and temperature dependences reported here with the postulated dynamic mechanism increases the probability that this mechanism is correct.
    Type of Medium: Electronic Resource
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