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1.
Subsequent to observations that pulmonary responses to antigen challenge are of different magnitudes in sensitized rats that are anesthetized with different drugs, we conducted studies to test whether the alterations in responses were due to changes in airway responsiveness to cholinergic or serotonergic challenge, opioid-receptor mediated events, or changes in mast cell mediator release. Immunoglobulin E-sensitized rats anesthetized with ketamine/urethan had larger changes in lung resistance and plasma histamine after pulmonary antigen challenge compared with rats anesthetized with fentanyl-droperidol. Blockade of opioid receptors with naloxone did not affect the responses. In unsensitized rats, airway responses to aerosolized methacholine were similar for the two anesthetics, indicating unchanged smooth muscle responsiveness; however, airway responses to intravenous serotonin were enhanced by ketamine and ablated by droperidol. We conclude that ketamine- and droperidol-induced alterations of pulmonary allergic responses are due to changes in sensitivity to serotonin and in mast cell mediator release. We speculate that mast cell mediator release may be modulated by a serotonin receptor-linked mechanism. 相似文献
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Changes in gas exchange characteristics and water use efficiency of mangroves in response to salinity and vapour pressure deficit 总被引:12,自引:0,他引:12
Summary Measurements were made of the photosynthetic gas exchange properties and water use efficiency of 19 species of mangrove in 9 estuaries with different salinity and climatic regimes in north eastern Australia and Papua New Guinea. Stomatal conductance and CO2 assimilation rates differed significantly between species at the same locality, with the salt-secreting species, Avicennia marina, consistently having the highest CO2 assimilation rates and stomatal conductances. Proportional changes in stomatal conductance and CO2 assimilation rate resulted in constant and similar intercellular CO2 concentrations for leaves exposed to photon flux densities above 800 mol·m-2·s-1 in all species at a particular locality. In consequence, all species at the same locality had similar water use efficiencies. There were, however, significant differences in gas exchange properties between different localities. Stomatal conductance and CO2 assimilation rate both decreased with increasing salinity and with increasing leaf to air vapour pressure deficit (VPD). Furthermore, the slope of the relationship between assimilation rate and stomatal conductance increased, while intercellular CO2 concentration decreased, with increasing salinity and with decreasing ambient relative humidity. It is concluded from these results that the water use efficiency of mangroves increases with increasing environmental stress, in this case aridity, thereby maximising photosynthetic carbon fixation while minimising water loss.Contribution No. 459 from the Australian Institute of Marine Science 相似文献
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D.L. Clough 《Life sciences》1984,35(19):1937-1946
Vanadate (VO4?3) produces a positive inotropic effect in rats and also promotes diuresis as well as natriuresis. Although the mechanism(s) of these effects is uncertain, in the kidney, VO4?3 may act through inhibition of (Na++K+)-ATPase activity, whereas in the heart, other or additional mechanisms are likely. Under the assay conditions used in the present study, microsomal (Na++K+)-ATPase activities from rat kidney cortex and medulla were inhibited to a greater extent than was left ventricular (Na++K+)-ATPase activity over a range of VO4?3 concentrations. The apparent dissociation constant for left ventricular (Na++K+)-ATPase (10.95 ± 1.26 × 10?7M VO4?3) was significantly greater than that of (Na++K+)-ATPase from the cortex (3.46±0.96×10?7 M VO4?3) or the medulla (3.32±0.7×10?7M VO4?3, N=6, P<.05) whereas there were no significant differences between the effects of VO4?3 on (Na++K+)-ATPase from the cortex and medulla. The greater inhibition by VO4, of (Na++K+)-ATPase from the cortex relative to that of the left ventricle, occurred over a range of Na+ and K+ concentrations, and K+ enhanced the inhibition by VO4?3 to a greater extent for (Na++K+)-ATPase from the cortex than the left ventricle. These results suggest that renal (Na++K+)-ATPase is more sensitive than left ventricular (Na++K+)-ATPase to inhibition by VO4?3 and would, therefore, be more likely to be modulated 相似文献
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Effects of low-chloride solutions on action potentials of sheep cadiac purkinje fibers 总被引:2,自引:0,他引:2
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The rapid repolarization during phase 1 of the action potential of sheep cardiac purkinje fibers has been attributed to a time- and voltage-dependent chloride current. In part, this conclusion was based on experiments that showed a substantial slowing of phase 1 when larger, presumably impermeant, anions were substituted for chloride in tyrode’s solution. We have re- examined the electrical effects of low-chloride solutions. We recorded action potentials of sheep cardiac purkinje fibers in normal tyrode’s solution and in low-chloride solutions made by substituting sodium propionate, acetylglycinate, methylsulfate, or methanesulfonate for the NaCl of Tyrode’s solution. Total calcium was adjusted to keep calcium ion activity of test solutions equal to that of control solutions. Propionate gave qualitatively variable results in preliminary experiments; it was not tested further. Low-chloride solutions made with the other anions gave much more consistent results: phase 1 and the notch that often occurs between phases 1 and 2 were usually unaffected, and the action potential duration usually increased. The only apparent change in the resting potential was a transient 3-6 mV depolarization when low-chloride solution was first admitted to the chamber, and a symmetrical transient hyperpolarization when chloride was returned to normal. If a time- and voltage-dependent chloride current exists in sheep cardiac purkinje fibers, our results suggest that it plays little role in generating phase 1 of the action potential. 相似文献
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The establishment of 3 specified-pathogen-free marmosets (Callithrix jacchus) during the period May 1969 to January 1973 is described. A brief history of the conventional breeding colony from which the animals were derived is given and hysterotomy and hand-rearing techniques are described. 相似文献
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Photosynthetic Adaptation of Solanum dulcamara L. to Sun and Shade Environments: II. Physiological Characterization of Phenotypic Response to Environment
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Photosynthetic and growth properties of Solanum dulcamara L. were studied under controlled environments. The 200 experimentally tested plants were clonal replicates of five field-collected individuals, three from fully exposed habitats and two from deeply shaded habitats. After 4 weeks of growth in one of eight environmental treatments, each plant was measured for leaf adaxial and abaxial conductance to water vapor, specific leaf weight, chlorophyll per square decimeter of leaf, photosynthetic unit size, light-saturated photosynthetic rate, total leaf area, and total leaf, stem, and root dry weights. Changes in light level influenced photosynthesis and growth of each plant more than changes in water availability or temperature. It is strongly suggested that the primary adaptive response of the tested individuals to changes in levels of light involves the regulation of leaf thickness. 相似文献
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