Acid-base regulation during thermal panting in the fowl (Gallus domesticus): comparison between breeds

1. The effects of high ambient temperatures on blood acid base status were studied in four breeds of fowl. 2. All breeds efficiently regulated body temperature below ambient temperature at 45 degrees C (Tb = 38.521 + 0.110Ta, at 25-45 degrees C). 3. A slight hypocapnia was partly compensated for by a decreased HCO3 concentration. This resulted in only a slight respiratory alkalosis at extreme temperatures (+0.021 and +0.042 pH units at 42 and 45 degrees C, respectively). 4. Changes in Paco2 were negatively correlated with tidal volume: Paco2 (torr) = 33.10390 - 1.17493 VT(ml); r = -0.925, P much less than 0.001. 5. The present findings are consistent with an hypothesis that modulation of tidal volume during thermal panting might play a major role in acid-base regulation.     

Mechanisms for the control of respiratory evaporative heat loss in panting animals.

Panting is a controlled increase in respiratory frequency accompanied by a decrease in tidal volume, the purpose of which is to increase ventilation of the upper respiratory tract, preserve alveolar ventilation, and thereby elevate evaporative heat loss. The increased energy cost of panting is offset by reducing the metabolism of nonrespiratory muscles. The panting mechanism tends to be important in smaller mammalian species and in larger species is supplemented by sweating. At elevated respiratory frequencies and body temperatures alveolar hyperventilation begins to develop but is accompanied by a decline in the control of carbon dioxide partial pressure in arterial blood, probably through central chemoreceptors. Most heat exchange takes place at the nasal epithelial lining, and venous drainage can be directed to a special network of arteries at the base of the brain whereby countercurrent heat transfer can occur, which results in selective brain cooling. Such a phenomenon has also been suggested in nonpanting species, including humans, and although originally thought to be a mechanism for protecting the thermally vulnerable brain is now considered to be one of the thermoregulatory reflexes whereby respiratory evaporation can be closely controlled in the interests of thermal homeostasis.     

Exchangers man the pumps: Functional interplay between proton pumps and proton-coupled Ca2+ exchangers

Tonoplast-localised proton-coupled Ca²⁺ transporters encoded by cation/H⁺ exchanger (CAX) genes play a critical role in sequestering Ca²⁺ into the vacuole. These transporters may function in coordination with Ca²⁺ release channels, to shape stimulus-induced cytosolic Ca²⁺ elevations. Recent analysis of Arabidopsis CAX knockout mutants, particularly cax1 and cax3, identified a variety of phenotypes including sensitivity to abiotic stresses, which indicated that these transporters might play a role in mediating the plant''s stress response. A common feature of these mutants was the perturbation of H⁺-ATPase activity at both the tonoplast and the plasma membrane, suggesting a tight interplay between the Ca²⁺/H⁺ exchangers and H⁺ pumps. We speculate that indirect regulation of proton flux by the exchangers may be as important as the direct regulation of Ca²⁺ flux. These results suggest cautious interpretation of mutant Ca²⁺/H⁺ exchanger phenotypes that may be due to either perturbed Ca²⁺ or H⁺ transport.Key words: abiotic stress, Ca²⁺ transport, Ca²⁺/H⁺ exchanger, H⁺-ATPase, Na⁺ transport, pH, salt stress, vacuoleCa²⁺ plays a fundamental role in the plant cell, functioning as a highly versatile second messenger controlling a multitude of cellular reactions and adaptive responses.^1,2 Ca²⁺ dynamics are maintained by precise interplay among transporters involved in its release from or uptake into Ca²⁺ stores. The vacuole, as the largest internal Ca²⁺ pool, is assumed to play a major role in Ca²⁺ signalling, and has been shown to be the source of Ca²⁺ release following various abiotic stresses such as cold and osmotic stress.^3,4 Rapid, stimulus-induced release of Ca²⁺ from the vacuole is attributable to selectively permeable Ca²⁺ channels, however, the identity of candidate genes encoding this mechanism remains contested.^5,6 Better understood, are the two major vacuolar uptake mechanisms; P-type Ca²⁺ pumps, including ACA4 and ACA11, which mediate high-affinity Ca²⁺ uptake, and a family of cation/H⁺ exchangers (CAX), responsible for lower-affinity but high-capacity Ca²⁺ uptake.^7,8 While Ca²⁺ pumps rely directly on the hydrolysis of ATP to drive Ca²⁺ uptake, Ca²⁺/H⁺ exchangers are energized indirectly by the pH gradient generated by electrogenic H⁺ pumps located on the tonoplast, including the vacuolar-type H⁺-ATPase (V-ATPase).⁹With the aim of further understanding the role of specific CAX isoforms in Arabidopsis, we and others have recently characterized CAX mutants and overexpression lines and observed a variety of phenotypes, including altered response to abiotic stresses.^10–14 While some phenotypes are identical among different CAX mutants, others are specific to individual lines.¹⁴ Moreover, these analyses have highlighted the interplay of these transporters with H⁺ pumps at both the tonoplast and the plasma membrane. Overexpression of CAX1 in Arabidopsis results in increased activity of the V-ATPase, whereas mutations in CAX1 cause a concomitant decrease in measured V-ATPase activity (Fig. 1).¹¹ Similar reductions in V-ATPase activity are also observed in cax2 and cax3 mutant plants but to a lesser extent,^12,13 and a significant reduction is observed in a cax1 cax3 double knockout line.¹³ At the plasma membrane, P-type H⁺-ATPase (P-ATPase) activity is increased in cax1 but decreased in cax3 (Fig. 1).¹⁴ Indeed cax3 lines appeared more sensitive to changes in the pH of the growth media.¹⁴ This implies that unlike cax1, cax3 is less efficient at cytoplasmic pH adjustment. Another intriguing observation is that activity of the H⁺-pyrophosphatase (H⁺-PPase) at the tonoplast is largely unaltered following CAX gene deletion. While overexpression of the Arabidopsis H⁺-PPase AVP1 leads to increased Ca²⁺/H⁺ exchange activity,^15,16 there is little alteration in H⁺-PPase activity following perturbed expression of CAX1 or CAX2.^11,12 Thus, this feedback interplay appears to exist only between exchangers and H⁺-ATPases.Open in a separate windowFigure 1Tonoplast H⁺-ATPase (V-ATPase) activity and plasma membrane H⁺-ATPase (P-ATPase) activity in wild type Arabidopsis (ecotype Col-0) and Arabidopsis lines with manipulated tonoplast Ca²⁺/H⁺ exchange activity. 35S::CAX1 and 35S::CAX2 denote lines that overexpress a constitutively active N-terminally truncated CAX1 or CAX2 construct driven by the CaMV 35S promoter in the cax1-1 or cax2-1 mutant background, respectively. V-ATPase H⁺-transport activity was measured by the ATP-dependent quenching of quinacrine fluorescence, and rates of bafilomycin-sensitive, vanadate-resistant hydrolytic activity of the V-ATPase were determined in isolated tonoplast membranes, as described in refs. ¹¹ and ¹³. Rates of vanadate-sensitive, bafilomycin- and azide-resistant hydrolytic activity of the P-ATPase were determined in isolated plasma membranes, as described in ref. ¹⁴. Results are shown as % of wild type (Col-0) ATPase activity and are means ± SE of 3–4 independent experiments. Data taken and modified from refs. ^11–14.The V-ATPase is important not only for maintenance of a pH gradient across the tonoplast, but also in maintenance of Golgi structure, endocytosis and secretory trafficking.^17,18 The V-ATPase is localised at the Golgi, endoplasmic reticulum and endosomes, in addition to the tonoplast.⁹ The det3 mutant, with a mutation in subunit C (VHA-C), has a 40–60% reduction in V-ATPase activity, but numerous severe developmental phenotypes.¹⁹ In contrast, the cax1 and cax1 cax3 mutants have a reduction in V-ATPase activity equivalent to det3 (Fig. 1), but the morphological phenotypes are not as pronounced.¹³ It is therefore likely that reduction of tonoplast Ca²⁺/H⁺ exchange primarily affects tonoplast V-ATPase activity, while V-ATPase activity in the secretory pathway is unperturbed. The V-ATPase is a multi-subunit protein and some of these subunit gene products appear to be either tonoplast-specific or tonoplast-enriched. Mutations in tonoplast subunits may cause defective V-ATPase activity only at the tonoplast.⁹ It will be of interest to see whether such tonoplast-specific V-ATPase mutants phenocopy the cax mutants, and possess perturbed Ca²⁺/H⁺ exchange activity and altered abiotic stress responses.CAX-mediated transport may alter both cytoplasmic and lumenal pH, as well as intracellular Ca²⁺ gradients. In the case of the V-ATPase, evidence is emerging for a role not only in the generation of a pH gradient across membranes, but also in the direct sensing of pH within the compartment,^20,21 creating a feedback mechanism which regulates pump activity. Thus, in cax1 lines, abnormal acidification of the lumen is detected by the V-ATPase resulting in a dampening of its activity. This would conserve ATP, which we postulate could be utilized to drive the tonoplast Ca²⁺ pump which itself is upregulated in cax1 as a compensatory mechanism to correct perturbations in the Ca²⁺ gradient.¹¹ In the case of cax1, this in turn may signal the P-ATPase to remove surplus H⁺ from the cytoplasm, triggering its upregulation (Fig. 1). However, not all CAX mutants show this complex H⁺ feedback mechanism.Co-ordinate downregulation of the V-ATPase in the cax1 mutant lines may also be a result of activity of the SOS2 kinase. This Ser/Thr kinase, which specifically interacts with the N-terminus of CAX1 resulting in Ca²⁺/H⁺ exchange activation,²² upregulates V-ATPase activity through interactions with the VHA-B regulatory subunit.²³ Loss of CAX1 may be signalling to the V-ATPase through changes in SOS2 activity resulting in a compensatory downregulation of the pump. It is tempting to speculate that SOS2 may signal the alteration in P-ATPase activity, as it is known to regulate other plasma membrane proteins, notably the Na⁺/H⁺ exchanger SOS1.²⁴ It will be interesting to determine if SOS2 and the P-ATPase interact directly. It is notable, however, that SOS2 does not appear to interact with CAX3,²² while P-ATPase activity is reduced in cax3 plants.¹⁴Our recent results indicate there are at least two modes by which Ca²⁺/H⁺ exchangers can mediate adaptive responses to stress: direct manipulation of cytosolic Ca²⁺ and indirect feedback of H⁺ flux (Fig. 2). For example, salt stress responses are likely controlled via the generation of a specific cytosolic Ca²⁺ signature, which mediates a downstream signalling pathway. CAX3 appears to be the principle isoform providing tonoplast Ca²⁺/H⁺ exchange in response to salt stress.¹⁴ Disruption of CAX3-mediated tonoplast Ca²⁺ transport and the alteration of cytosolic Ca²⁺ dynamics may therefore alter the plant''s normal response to salt stress (Fig. 2). Maintenance of H⁺ gradients at both the vacuole and plasma membrane are also critical for salt tolerance, such that salt treatment upregulates V-ATPase and P-ATPase activity.²⁵ This energizes Na⁺ efflux from the cytosol mediated by Na⁺/H⁺ exchangers at the plasma membrane and the tonoplast.^24,26 Therefore downregulation of H⁺ pumps at both membranes in the cax3 mutant is likely to perturb the ability of the cell to remove Na⁺ (Fig. 2). Further analysis of cax mutants, P-ATPase mutants, and tonoplast-specific V-ATPase mutants will be required to determine whether many of the phenotypes resulting from lack of Ca²⁺/H⁺ exchange activity are due to altered Ca²⁺ transport or H⁺ transport.Open in a separate windowFigure 2Model of tonoplast Ca²⁺/H⁺ exchanger interaction with H⁺ pumps in response to salt stress. (A) In response to NaCl treatment, an elevation in cytosolic Ca²⁺ will occur, possibly due to vacuolar Ca²⁺ release.³ Increased CAX3-mediated Ca²⁺/H⁺ exchange activity¹⁴ will sequester excess Ca²⁺ into the vacuole. CAX3 may be involved in the generation of a specific Ca²⁺ signature that is recognised by the cell to mediate downstream stress responses. In addition, salt stress will lead to upregulation of H⁺ pumps at both the plasma membrane and the tonoplast (P-ATPase and V-ATPase)²⁵ which will in turn energize Na⁺/H⁺ exchange activity encoded by SOS1 and NHX1, promoting Na⁺ efflux from the cell. Increased V-ATPase activity may also upregulate Ca²⁺/H⁺ exchange. Activity of SOS1 requires activation by the kinase SOS2²⁴ which may also regulate tonoplast Na⁺/H⁺ exchange and V-ATPase activity.^23,24 (B) In a cax3 knockout mutant experiencing salt stress, the cytosolic Ca²⁺ elevation may be sustained due to reduced vacuolar Ca²⁺ sequestration and normal salinity-induced Ca²⁺ signalling pathways may be perturbed. Lack of CAX3 downregulates both P-ATPase and V-ATPase activity¹⁴ thereby reducing energization of the plasma membrane and tonoplast Na⁺/H⁺ exchangers and reducing Na⁺ efflux from the cell. Some energization of H⁺-coupled processes at the vacuole may be maintained by residual H⁺-pyrophosphatase (V-PPase) activity.The phenomenon observed between tonoplast Ca²⁺/H⁺ exchangers and H⁺ pumps at both the tonoplast and plasma membranes, suggesting a co-ordinate regulation between several transporters, is not solely restricted to this family of transporters. It is a common observation emerging from recent research on the manipulation of tonoplast transporters. Several labs have reported unpredictable phenotypes associated with ectopic expression of tonoplast proteins.^26–28 Until we understand the significance of these types of unexpected interactions, it is naïve to believe that engineering plants will provide predictable results.     

Mechanistic and phenomenological features of proton pumps in the respiratory chain of mitochondria

Various direct, indirect (kinetic and thermodynamic), and combined mechanisms have been proposed to explain the conversion of redox energy into a transmembrane protonmotive force (p) by enzymatic complexes of respiratory chains. The conceptual evolution of these models is examined. The characteristics of thermodynamic coupling between redox transitions of electron carriers and scalar proton transfer in cytochromec oxidase and its possible involvement in proton pumping is discussed. Other aspects dealt with in this paper are: (i) variability of H⁺/e ^– stoichiometries, in cytochromec oxidase and cytochromec reductase and its mechanistic implications; (ii) possible models by which the reduction of dioxygen to water at the binuclear heme-copper center of protonmotive oxidases can be directly involved in proton pumping. Finally a unifying concept for proton pumping by the redox complexes of respiratory chain is presented.     

家鸡腺苷琥珀酸裂解酶基因多态性与肌苷酸含量的关联及其与红原鸡的亲缘关系

根据腺苷琥珀酸裂解酶(adenylosuccinate lyase, ADSL)基因外显子2的序列设计引物, 用PCR-SSCP的方法对隐性白羽鸡、丝羽乌骨鸡、白耳鸡、藏鸡以及红色原鸡两个亚种进行了单核苷酸多态性分析, 并检测到了多态性, 表现为3种基因型, 对两种纯合子进行直接测序, 结果发现3484位碱基处发生C→T突变。对3种基因型的肌肉肌苷酸含量的最小二乘分析结果显示TT型(突变型)个体的肌肉肌苷酸含量极显著地高于CT型、显著地高于CC型个体, CT型个体也稍高于CC型, 但差异不显著, 初步推测该位点可能与肌肉肌苷酸含量有关。根据该多态位点的基因频率, 基于Nei氏的遗传距离运用NJ聚类法构建系统发生树, 进行家鸡与原鸡的亲缘关系分析, 结果发现, 丝羽乌骨鸡与白耳鸡的亲缘关系最近, 藏鸡和中国红原鸡亚种的亲缘关系也较近, 中国地方家鸡品种与中国红原鸡亚种的亲缘关系较近,而与泰国红色原鸡的亲缘关系较远,隐性白羽鸡与原鸡亲缘关系最远, 初步得出中国家鸡有自己独自的血缘来源的结论。     

Respiratory cycle related EEG changes: Modified respiratory cycle segmentation

Respiratory cycle related EEG change (RCREC) is characterized by significant relative EEG power changes within different stages of respiration during sleep. RCREC has been demonstrated to predict sleepiness in patients with obstructive sleep apnoea and is hypothesized to represent microarousals. As such RCREC may provide a sensitive marker of respiratory arousals. A key step in quantification of RCREC is respiratory signal segmentation which is conventionally based on local maxima and minima of the nasal flow signal. We have investigated an alternative respiratory cycle segmentation method based on inspiratory/expiratory transitions. Sixty two healthy paediatric participants were recruited through staff of local universities in Bolivia. Subjects underwent attended polysomnography on a single night (Compumedics PS2 system). Studies were sleep staged according to standard criteria. C3/A2 EEG channel and time-locked nasal flow (thermistor) were used in RCREC quantification. Forty Seven subjects aged 7–17 (11.4 ± 3) years (24M:23F) were found to have usable polysomnographs for the purpose of RCREC calculation. Respiratory cycles were segmented using both the conventional and novel (transition) methods and differences in RCREC derived from the two methods were compared in each frequency band. Significance of transition RCREC as measured by Fisher's F value through analysis of variance (ANOVA) was found to be significantly higher than the conventional RCREC in all frequency bands (P < 0.05) but beta. This increase in statistical significance of RCREC as demonstrated with the novel transition segmentation approach suggests better alignment of the respiratory cycle segments with the underlying physiology driving RCREC.     

Morphometry of the galliform cecum: A comparison between Gambel's quail and the domestic fowl

Summary Tissues from the proximal, middle, and distal regions of the ceca of Gambel's quail and domestic fowl were examined by scanning and transmission electron microscopy. Cellular and subcellular structures, including epithelial cell height, mitochondrial volume fraction, microvillous surface area, proportion of goblet cells, and junctional complex characteristics, were quantified by a variety of stereologic procedures and other measurement techniques. The mucosal surface of quail cecum shows a much more highly developed pattern of villous ridges and flat areas than that of fowl cecum. The fowl has significantly greater cell heights than the quail in all cecal regions. The mitochondrial volume fraction does not differ significantly with species or region, but mitochondria are concentrated on the apical side of the nucleus. In both species, the proximal cecal region has the greatest microvillous surface area. All 3 components of junctional complexes, including zonula occludens, zonula adhaerens, and macula adhaerens, are quantified. When all factors are considered, the quail cecum appears to have morphological characteristics consistent with a greater potential capacity for absorption than the fowl cecum.     

普通齿蛉幼虫的呼吸系统及呼吸行为

研究了普通齿蛉Neoneuromus ignobilis Navás幼虫的呼吸系统及其呼吸行为。结果表明:普通齿蛉幼虫为全气门式(10对气门)呼吸系统,前中胸、中后胸之间、腹部8节各有1对气门,腹部8节各有气管鳃1对,前6对细短,管状,有较短绒毛,后2对气管鳃较粗长,呈羽毛状。腹部1～7节各有1对毛簇,第8腹节无毛簇。侧纵干气管较粗,4束,自前胸前缘部分成左右2组,每组两根侧纵干气管,向胸腹部延伸,二级气管分别伸达各个气门和毛簇,腹部每节由毛簇处的二级气管分支而来的三级气管相连或延伸至消化道等处。气管鳃中无气管。有毛簇呼吸、气门呼吸和体壁呼吸3种呼吸方式,在水中以毛簇呼吸为主,在陆上进行气门呼吸和体壁呼吸。     

Pump-like channelrhodopsins: Not just bridging the gap between ion pumps and ion channels

Channelrhodopsins are microbial rhodopsins that work as light-gated ion channels. Their importance has become increasingly recognized due to their ability to control the membrane potential of specific cells in a light-dependent manner. This technology, termed optogenetics, has revolutionized neuroscience, and numerous channelrhodopsin variants have been isolated or engineered to expand the utility of optogenetics. Pump-like channelrhodopsins (PLCRs), one of the recently discovered channelrhodopsin subfamilies, have attracted broad attention due to their high sequence similarity to ion-pumping rhodopsins and their distinct properties, such as high light sensitivity and ion selectivity. In this review, we summarize the current understanding of the structure-function relationships of PLCRs and discuss the challenges and opportunities of channelrhodopsin research.