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1.
Avian testicular receptors for gonadotropins show a species-specificity similar to mammalian receptors for the binding affinity to gonadotropins of various origins. In the affinity-capacity relationships, avian FSH receptors are classified in the same group with chelonians, that is, they exhibit relatively low affinity and high capacity. FSH receptors of the Japanese quail resemble the rat receptor with respect to the temperature-dependence of affinity in the low-temperature range, but also resemble reptilian or amphibian receptors with respect to binding affinities in the middle- to high-temperature range. We conclude that avian gonadotropin receptors have some characteristics of homeothermic vertebrates, but still retain characteristics of poikilothermic groups.  相似文献   

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Intrapulmonary chemoreceptors (IPC) are highly responsive respiratory chemoreceptors that innervate the lungs of birds and diapsid reptiles. IPC are stimulated by low levels of lung Pco(2), inhibited by high levels of lung Pco(2), and their vagal afferents serve as a sensory limb for reflex adjustments of breathing depth and rate. Most IPC exhibit both phasic and tonic sensitivity to CO(2), and spike frequency adaptation (SFA) contributes to their phasic CO(2) responsiveness. To test whether CO(2) responsiveness and SFA in IPC is modulated by a Ca(2+)-linked mechanism, we quantified the role of transmembrane Ca(2+) fluxes and Ca(2+)-related channels on single-unit IPC function in response to phasic changes in inspired Pco(2). We found that 1) broad-spectrum blockade of Ca(2+) channels using cadmium or cobalt and blockade of L-type Ca(2+) channels using nifedipine increased IPC discharge; 2) activation of L-type Ca(2+) channels using BAY K 8644 reduced IPC discharge; 3) blockade of Ca(2+)-activated potassium channels using charybdotoxin (antagonist of large-conductance Ca(2+)-dependent K(+) channel) increased IPC discharge, but neither charybdotoxin nor apamin affected SFA; and 4) blockade of chloride channels, including Ca(2+)-activated chloride channels, with niflumic acid decreased IPC discharge at low Pco(2) and increased IPC discharge at high Pco(2), resulting in a net attenuation of the IPC CO(2) response. We conclude that Ca(2+) influx through L-type Ca(2+) channels has an inhibitory effect on IPC afferent discharge and CO(2) sensitivity, that spike frequency adaptation is not due to apamin- or charybdotoxin-sensitive Ca(2+)-activated K(+) channels in IPC, and that chloride channels blocked by niflumic acid help modulate IPC CO(2) responses.  相似文献   

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Diambra L  Guisoni N 《Cell calcium》2005,37(4):321-332
We focused our attention on Ca(2+) release from the endoplasmic reticulum through a cluster of inositol(1,4,5)-trisphosphate (IP(3)) receptor channels. The random opening and closing of these receptors introduce stochastic effects that have been observed experimentally. Here, we present a stochastic version of Othmer-Tang model (OTM) for IP(3) receptor clusters. We address the average behavior of the channels in response to IP(3) stimuli. In our stochastic simulation we found that the fraction of open channels versus [IP(3)] follows a Hill curve, whose associate Hill coefficient increases when intracellular Ca(2+) level increase. This finding suggests that feedback from cytosolic Ca(2+) plays a key role in the channel response to IP(3). We also study several aspects of the stochastic properties of Ca(2+) release and we compare with experimental observations.  相似文献   

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We made unilateral chemical (10- or 50-nl microinjections; 4.7 mM kainic acid) or electrolytic (5-15 mA; 15 s) lesions in a region of the rostral ventrolateral medulla (VLM) caudal to the retrotrapezoid nucleus in 10 decerebrate, paralyzed, vagotomized, and servo-ventilated cats. The lesions were 3.0-4.2 mm lateral to the midline, within 2 mm caudal to the facial nucleus, and within 2.5 mm of the VLM surface. Four control injections (mock cerebrospinal fluid and fluorescent beads alone) produced small and inconsistent effects over 3-5 h. The predominant effect of the lesions was a significant decrease in baseline integrated phrenic nerve amplitude (PNA) (apnea in 2 cases), total respiratory cycle duration, and the response to increased CO2 (slope < 15% of control in 3 cases). The respiratory-related peak amplitude of the integrated sympathetic signal, blood pressure, and the sympathetic nerve activity response to CO2 were also decreased after the majority of lesions. Not all lesions produced all effects, and some lesions resulted in increased PNA and respiratory cycle duration. The lesioned region appears functionally to represent a caudal extension of the retrotrapezoid nucleus containing neurons necessary for normal baseline PNA and CO2 sensitivity. In addition, it contains neurons involved in the determination of resting respiratory frequency and normal sympathetic activity and blood pressure. The pattern of mixed responses among animals suggests that a heterogeneity of function is present within a relatively small VLM region.  相似文献   

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Ventilatory responses to CO2 inhalation and CO2 infusion were compared in the awake dog. The CO2 was introduced directly into the systemic venous blood via a membrane gas exchanger in a femoral arteriovenous shunt circuit, and the extracorporeal blood flow, QX, was maintained constant at one of two rates: low, 0.5 l/min; or high, 2.0 l/min. A total of 13 experiments was performed in four dogs comprising 50 control and 25 inhalation and infusion observations at each of the two flow rates. Comparison of CO2-response curve slopes, S = delta V E/delta PaCO2, between CO2 inhalation and infusion showed no significant difference either within or between flow rates. The mean value of S for all conditions was 1.88 l/min per Torr with a 95% confidence interval of 1.66 -2.14. An independent additive ventilatory drive amounting to 28% of low-flow control VE was found at the highflow rate. We conclude that at constant blood flow the responses to both CO2 inhalation and infusion are hypercapnic and not significantly different.  相似文献   

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The chemical gating of single-gap junction channels was studied by the dual whole-cell voltage-clamp method in HeLa cells transfected with connexin43 (HeLa43) and in fibroblasts from sciatic nerves. Junctional current (Ij), single-channel conductance, and Ij kinetics were studied in cell pairs during CO2 uncoupling and recoupling at small transjunctional voltages (Vj < 35 mV: Vj gating absent) and at high Vj (Vj > 40 mV: Vj gating strongly activated). In the absence of Vj gating, CO2 exclusively caused Ij slow transitions from open to closed channel states (mean transition time: approximately 10 ms), corresponding to a single-channel conductance of approximately 120 pS. At Vj > 40 mV, Vj gating induced fast Ij flickering between open, gamma j(main state), and residual, gamma j(residual), states (transition time: approximately 2 ms). The ratio gamma j(main state)/gamma j(residual) was approximately 4-5. No obvious correlation between Ij fast flickering and CO2 treatment was noticed. At high Vj, in addition to slow Ij transitions between open and closed states, CO2 induced slow transitions between residual and closed states. During recoupling, each channel reopened by a slow transition (mean transition time: approximately 10 ms) from closed to open state (rarely from closed to residual state). Fast Ij flickering between open and residual states followed. The data are in agreement with the hypothesis that gap junction channels possess two gating mechanisms, and indicate that CO2 induces channel gating exclusively by the slow gating mechanism.  相似文献   

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This study uses an awake unidirectionally ventilated avian preparation to examine the effects of dynamic CO2 signals on the respiratory drive. Results show that minute ventilation is affected by both 1) mean CO2 level and 2) amplitude of CO2 oscillations at the frequency of breathing. An increase in mean CO2 level increased minute ventilation. Comparisons of the effects of CO2 oscillations at the same mean CO2 level, however, showed minute ventilation to be less with the larger amplitudes of oscillations than with smaller ones. Graphs of minute ventilation (V) versus mean CO2 for families of oscillation sizes (0.5%, 1% and 2%) showed that the ventilatory sensitivity (slop) was least for the 2% oscillations and greatest for the 0.5% oscillations. Therefore, a static model for the respiratory regulator is not adequate. However, the apneic level of CO2 (V = O intercept) was independent of the size of the CO2 oscillations.  相似文献   

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ErbB2 and ErbB3 receptors belong to the epidermal growth factor receptor family. The members of this family are able to form homo- and heterodimers that trigger diverse downstream signalling concerned to multiple cellular events. In the absence of a ligand, ErbB3 adopts a characteristic tethered conformation, which differs from ErbB2 extended conformation. In this work, transmission electron microscopy (TEM) and dynamic light scattering (DLS) have been used to characterize the conformational features and the size of ErBb2 and ErbB3 receptors. Two main objectives are presented. The first one is to evaluate the use of TEM as a tool for structural studies for this family of receptors. The low molecular weight of these proteins represents a challenging purpose for TEM studies. The other one is to search for a relationship between the results obtained by TEM and those obtained for the hydrodynamic size measured by DLS. This comparison has allowed us to identify the conformational differences of the receptors and to anticipate the use of these experimental techniques for the study of the ligand activated heterodimerization, a process related to a significant number of human malignancies.  相似文献   

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Summary Single-unit vagal afferent recordings were made on 55 intrapulmonary receptors in 15 anesthetized or decerebrate bullfrogs. Intrapulmonary CO2 concentration and intrapulmonary pressure were controlled independently by unidirectionally ventilating the lungs. No CO2 receptors (insensitive to stretch of the lung) of the kind reported in birds and reptiles were found; all 55 receptors were mechano-sensitive. Of these mechanoreceptors, 39 adapted slowly to inflation of the lung and 16 adapted rapidly. Thirtythree of the slowly-adapting receptors and 15 of the rapidly adapting receptors decreased their discharge frequency as intrapulmonary CO2 concentration was increased. Inflating the lung enhanced CO2 sensitivity. The results indicate that the frog possesses CO2-sensitive pulmonary mechanoreceptors similar to those of mammals and reptiles.Abbreviations P ip intrapulmonary pressure - fractional inspired concentration of CO2 The authors wish to thank Dalyn Wilson for his help in gathering the experimental animals and for his technical assistance. The study was supported in part by a grant-in-aid from the American Heart Association, Kansas Affiliate, Inc. Contribution No. 78-185-J Department of Anatomy and Physiology, KAES, Kansas State University, Manhattan, Kansas 66506, USA.  相似文献   

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Selection pressures due to parasitism play an important role in driving the evolution of life history traits of birds in general and of behaviour at the nest in particular. Eggshell bacterial load has been shown to predict hatching failure (i.e. the probability of embryo infection) but the relationships between the bacterial environment of the nest and life history characteristics of birds remain poorly investigated. We explored interspecific variation in eggshell bacterial load of mesophilic bacteria, Enterococcus spp., Staphylococcus spp. and Enterobacteriaceae groups across 24 bird species and assessed whether bacterial load is associated with breeding traits. Interspecific variation was much higher than intraspecific variation for all measures of bacterial load even after controlling for annual variation. Thus, we were able to assess the correlation between bacterial community characteristics and life history traits. After correcting for phylogenetic effects, we found that nest type, the use of feathers or plants as lining material, and incubation behaviour explained a significant proportion of the variance in bacterial communities on eggshells. The strength of these associations depended on study year, suggesting an important role of environmental conditions for eggshell bacterial load or community. Overall, these results suggest that bacteria on eggshells are associated with bird species traits, probably because birds are mediating the deleterious effect of eggshell microbes through behavioural traits that modify bacterial load.  相似文献   

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Garter snakes increase ventilation in response to elevated venous PCO2 without a concomitant rise in arterial PCO2 (Furilla et al. Respir. Physiol. 83: 47-60, 1991). Elevating venous PCO2 will increase the PCO2 gradient between pulmonary arterial blood and intrapulmonary gas during inspiration, leading to a greater rate of rise of intrapulmonary CO2 after inspiration. Because the lung contains CO2-sensitive receptors, I assessed the effect of the rate of rise of intrapulmonary CO2 on ventilation in unidirectionally ventilated snakes. CO2 concentration was altered using a digital gas mixer connected to a personal computer. Breathing frequency was highly correlated with the rate of rise intrapulmonary CO2 but only slightly affected by peak intrapulmonary CO2. On the other hand, tidal volume was more closely related to peak intrapulmonary CO2 than to the rate of rise of CO2. Bilateral pulmonary or cervical vagotomy nearly eliminated the ventilatory response associated with altered CO2 rise times but had little influence on the tidal volume response to the rate of rise of CO2. The mechanism whereby breathing frequency is controlled by the rate of rise of intrapulmonary CO2 is likely to originate with intrapulmonary chemoreceptors and may be important in the control of breathing during exercise.  相似文献   

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The avian embryo exchanges the oxygen and carbon dioxide withthe ambient air by diffusion. The respiratory organ is the chorioallantois,endowed with a rich circulation. Between ambient air and chorioallantoiccapillary blood are interposed the porous shell fibrous shellmembranes, and the chorioendothelium which compose the diffusionbarrier. The air cell is formed between the two shell membranesin the blunt end of the egg. The diffusion barrier is dividedinto an outer barrier (shell plus outer membrane) and an innerbarrier (inner membrane plus chorioendothelium and capillaryblood). The resistance to gas diffusion (the reciprocal of thediffusive conductance) in the outer barrier is almost fixedthroughout incubation while that in the inner barrier decreasesas the embryo develops. Because of the fixed outer barrier conductance,the embryo is obliged to take up oxygen under hypoxic conditionsagainst increasing metabolism with development and encountersa relative respiratory acidosis. In connection with the diffusivehypoventilation caused by the fixed outer barrier conductancethe respiratory factors of the allantoic circulation changeprogressively with development to moderate the restraint ofgas exchange through the shell. Blood oxygen capacity and hemoglobinincrease with development in association with an increase inerythrocyte count and hematocrit value. In addition, a progressiveleftward shift of the oxygen dissociation curve occurs. Theincreases in the allantoic blood flow and chorioallantoic capillaryvolume contribute to the increasing conductance of the innerbarrier. Furthermore regulation of acid base balance is inferredin the developing embryo.  相似文献   

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