The Journal of physiology
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The Journal of physiology · Mar 1983
Adapting lights and lowered extracellular free calcium desensitize toad photoreceptors by differing mechanisms.
Extracellular recordings were made across the outer segment layer of isolated, superfused toad retinas. Under these recording conditions, the photovoltage reflects primarily the current flowing through the outer-segment membrane of red rods. In normal toad Ringer solution, a dim conditioning flash desensitized a test flash response. ⋯ These results can be understood in terms of the Ca2+ hypothesis of transduction (Hagins & Yoshikami, 1974) if it is assumed that lowered [Ca2+]o exposes an endogenous Ca2+ buffer. The data also provide evidence for a role of Na+/Ca2+ exchange in regulating intracellular Ca2+ concentration in the toad photoreceptor. A quantitative model based on these assumptions is derived and compared with the experimental data.
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The Journal of physiology · Feb 1983
Structure-activity relationships for some substance P-related peptides that cause wheal and flare reactions in human skin.
Substance P (6.25-25 p-mole) produced dose-dependent flare and wheal responses when injected intradermally into the volar surface of the human forearm. The maximum flare response was obtained within the first 3 min of injection and declined thereafter. The wheal response reached a maximum after 12 min following the injection. ⋯ Pre-treatment of the skin with capsaicin reduced the flare but not the wheal response to intradermal injection of histamine. The results are discussed in relation to the mechanism of the 'axon reflex' vasodilatation in skin. This is thought to involve mast cells in addition to substance P-containing primary afferent neurones.
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The Journal of physiology · Dec 1982
The rate of rise of alveolar carbon dioxide pressure during expiration in man.
1. The purpose of the study was to see whether the rate of rise of alveolar PCO2 (PA, CO2) in expiration was directly proportional to the rate of pulmonary elimination of CO2 (VCO2) in man in the steady state. 2. Alveolar ventilation at rest and during exercise in man was calculated from the difference between total ventilation and dead space ventilation, and from the ratio of the rate of pulmonary CO2 elimination to the mean expired alveolar CO2 (total) fraction. ⋯ In the first, a pattern of respiration with constant expiratory flow in each breath brought expiratory alveolar profiles to the outermost end of the airway. In the second method, the early part of the alveolar PCO2 during normal expiration was calculated from airway PCO2 and expired volume. 4. The data obtained with both methods show that, in the steady state, expiratory alveolar PCO2 rises at a rate which is directly proportional to the rate of CO2 production.
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The Journal of physiology · Oct 1982
Closely coupled excitation of gamma-motoneurones by group III Muscle afferents with low mechanical threshold in the cat.
1. The reflex responses of gamma-motoneurones to discharges of muscle receptors innervated by Group III axons have been examined in hind-limb muscles of decerebrated and spinal cats.2. Electrical stimulation of the gastrocnemius medialis nerve at a strength sufficient to excite Group III axons caused excitation of gastrocnemius lateralis or soleus gamma-motoneurones. ⋯ Receptive fields of all Group III units were confined to either the proximal third or distal third of gastrocnemius medialis or, in a few instances, the Achilles tendon.11. We conclude that discharges in Group III axons from receptors which respond to non-noxious, low threshold mechanical stimuli cause a tightly coupled excitation of gamma-motoneurones. The likely contribution of this reflex to the control of movement is discussed.
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The Journal of physiology · Sep 1982
Comparative StudyThe response of the hind-limb vascular bed of the rabbit to sympathetic stimulation and its modification by pregnancy.
1. Pressure-flow relationships in the hind limb, perfused with blood at a series of constant flows, have been compared in primigravid and virgin rabbits following section of the lumbar sympathetic chain. 2. In the absence of sympathetic stimulation perfusion pressure was lower (P less than 0.05) in the pregnant rabbits at all levels of flow to the leg. 3. ⋯ Examination of the pressure-flow curves suggests that when, as in these experiments, flow is held constant, the ability of sympathetic stimulation to increase the resistance to blood flow is reduced in pregnancy. However, if these pressure-flow curves are used to predict the change of flow that would occur at a constant perfusion pressure, the response to sympathetic stimulation appears to be greater in pregnancy. 7. Further analysis of the findings, based on certain assumptions, suggests that differences between the pressure-flow curves of pregnant and non-pregnant animals during sympathetic stimulation are due in the main to either a differing size of the unstimulated vascular beds or a differing compliance of their vessel walls, rather than to any intrinsic alteration in their response to sympathetic stimulation.