Membrane electrical parameters in turtle bladder measured using impedance-analysis techniques

Summary Equivalent-circuit impedance analysis experiments were performed on the urinary bladders of freshwater turtles in order to quantify membrane ionic conductances and areas, and to investigate how changes in these parameters are associated with changes in the rate of proton secretion in this tissue. In all experiments, sodium reabsorption was inhibited thereby unmasking the electrogenic proton secretion process. We report the following: (1) transepithelial impedance is represented exceptionally well by a simple equivalent-circuit model, which results in estimates of the apical and basolateral membrane ionic conductances and capacitances; (2) when sodium transport is inhibited with mucosal amiloride and serosal ouabain, the apical and basolateral membrane conductances and capacitances exhibit a continual decline with time; (3) this decline in the membrane parameters is most likely caused by subtle time-dependent changes in cell volume, resulting in changes in the areas of the apical and basolateral membranes; (4) stable membrane parameters are obtained if the tissue is not treated with ouabain, and if the oncotic pressure of the serosal solution is increased by the addition of 2% albumin; (5) inhibition of proton secretion using acetazolamide in CO₂ and HCO ₃ ^– -free bathing solutions results in a decrease in the area of the apical membrane, with no significant change in its specific conductance; (6) stimulation of proton transport with CO₂ and HCO ₃ ^– -containing serosal solution results in an increase in the apical membrane area and specific conductance. These results show that our methods can be used to measure changes in the membrane electrophysiological parameters that are related to changes in the rate of proton transport. Notably, they can be used to quantify in the live tissue, changes in membrane area resulting from changes in the net rates of endocytosis and exocytosis which are postulated to be intimately involved in the regulation of proton transport.     

Constitutive and transport-related endocytotic pathways in turtle bladder epithelium

Summary Proton secretion in the urinary bladder of the fresh-water turtle is mediated by a proton pump located in the apical membrane of a population of cells characteristically rich in carbonic anhydrase. Earlier studies have demonstrated that these cells exhibit apical-membrane endocytotic and exocytotic processes which are thought to be involved in the regulation of the rate of proton transport via alterations in the number of pumps within the apical membrane. In this study, we sought to characterize these processes using two different methods. Analysis of transepithelial impedance yielded estimates of membrane capacitance which could be related to membrane area, thereby allowing one to monitor net changes in apical-membrane area resulting from changes in the net rates of endo-and exocytosis. Uptake of the fluid-phase marker FITC-dextran provided a measure of net extracellular volume uptake which was related to net rates of endocytosis. Our major conclusions are summarized as follows. The bladder cells exhibit a high baseline rate of endocytosis which appears to be a constitutive process similar to pinocytosis. This process is completely inhibited when ambient temperature is reduced to 15°C. In addition, serosal application of 0.5mm acetazolamide causes a transient increase in the rate of endocytosis, concomitant with a decrease in the rate of transport. Reduction of ambient temperature to 15°C reduces the rate of acetazolamide-induced endocytosis, but does not abolish it. Addition of 1mm serosal azide not only prevents the acetazolamide-induced increase in endocytosis, but also prevents the decrease in transport caused by acetazolamide. Azide has no effect on the baseline rate of endocytosis, nor does it prevent inhibition of carbonic anhydrase by acetazolamide. The specificity of azide, coupled with the different temperature sensitivities, demonstrate that the constitutive and transport-dependent endocytotic pathways are distinct processes. The observation that azide prevents both the acetazolamide-induced increase in endocytosis and the decrease in transport strongly supports the notion that endocytosis of proton-pump-containing membrane is requisite for the inhibition of transport by acetazolamide. Finally, the results also demonstrate that acetazolamide does not inhibit proton secretion simply by inhibiting carbonic anhydrase.     

Mechanical impedance increases aluminium tolerance of soybean (Glycine max) roots

The effect of aluminium (Al) on root elongation was studied in solution culture and sand culture. Compared to solution culture, in sand culture a ten times higher Al supply was necessary to inhibit root elongation to a comparable degree. This was due to a much lower Al uptake into the 5 mm root tips in sand culture. Fe concentrations in root tips were also lower in sand culture. Ca concentrations were higher and less depressed by Al, whereas Mg and K concentrations were not affected by the culture substrate. Regressions of Al concentrations in root tips versus inhibition of root elongation by Al revealed root damage at lower Al concentrations in sand culture. The effect of culture substrate on Al tolerance was independent of N source and could also be shown in flowing solution culture with and without sand. The results indicate that mechanical impedance in sand culture decreased Al uptake. This may be due to enhanced exudation of organic complexors thus reducing activites of monomeric Al species.     

Complete mechanical impedance increases the turgor of cells in the apex of pea roots

In this paper we describe an experimental approach which allows turgor (p) in an impeded root to be measured without the need to remove the root from the impeding environment. The maximum axial growth pressure (σ_max) generated by completely impeded pea (Pisum sativum L.) roots was measured using a novel apparatus incorporating a force transducer. The apparatus was designed so that it was possible to gain access to the impeded root with the microcapillary of a pressure probe and so obtain in situ measurements of P. Turgor in cells in the apical region of impeded roots was 0.78 MPa, compared with 0.55 MPa in unimpeded roots. In impeded roots, σ_max was 0.52 MPa, showing that the pressure component resulting from cell wall tension (W, where W=P–σ) decreased from 0.55 to 0.26 MPa as the roots became impeded. When impeded roots were removed from the apparatus, there was no decrease in P over the following 90 min. Impedance did not cause P to change in the non-elongating part of the roots further from the apex.     

An impedimetric method for rapid screening of cosmetic preservatives

An efficient impedance method was developed for rapid evaluation of cosmetic preservatives. The method used decimal reduction time or D-value to assess preservative efficacies. The D-value, which was calculated from the plot of Log CFU ml^–1 versus time by linear regression analysis, could be obtained within 48 h. Thus, the time required for the challenge test was reduced from 4–8 weeks with the standard procedures (eg US Pharmacopeia), to 2 days with the current method. A calibration curve (r=-0.95) was established by plotting the Log CFU ml^–1 versus capacitance detection time (DT) of 108 samples. With the calibration, CFU can be estimated directly from the impedance test without plating. Two commercial biocides and several other chemicals were evaluated in a shampoo by the impedance procedure againstPseudomonas aeruginosa. The D-values obtained from the impedance test were not significantly different from those produced by the conventional plate count method. The technique was found to be particularly useful when screening a large number of compounds to find novel preservatives and synergistic preservative combinations.     

USE OF BIOELECTRICAL IMPEDANCE ANALYSIS TO ASSESS BODY COMPOSITION OF SEALS

Abstract: Bioelectrical impedance analysis (BIA) measures resistance and reactance of a current as it passes through an organism. The validity of using BIA as a tool to measure body water content, and hence body composition and condition, was tested on harp and ringed seals. The resistance and reactance readings from BIA were compared to estimates of total body water (TBW) determined via tritiated water dilution. The relationship between resistance and TBW (% of body mass) was linear after logarithmic transformation and the two variables were highly correlated. We describe the electrode configuration and placements which provide reliable results in these seals. Our findings indicate that BIA has considerable potential as an inexpensive, rapid, and reliable technique for estimating body composition of phocid seals.     

人类小腿肌肉对运动训练生理响应的电学特性研究

目的 运动训练已被证明能够改善许多慢性肌肉功能疾病,被用于治疗衰老型肌萎缩。本文采用电阻抗成像(electrical impedance tomography,EIT)研究人类小腿肌肉对运动训练生理响应的电学特性,旨在使用EIT方法可视化运动训练对人类小腿响应肌肉隔室内肌肉纤维体积增加的效果。方法 实验对象被要求在连续5个实验日进行左、右腿单侧提踵训练,应用EIT检测每日运动训练前和运动训练后小腿肌肉的电导率分布。为了定量分析运动训练对响应肌肉隔室的作用,使用配对样本t检验分析EIT重建图像的空间平均电导率<σ>。结果 运动训练后,由小腿腓肠肌组成的M₁肌肉隔室空间平均电导率<σ>_M1显著增加。此外,连续5个实验日的EIT测量结果显示,运动训练前的空间平均电导率<σ^pre>_M1呈上升趋势。所有实验对象在实验日1早晨进行实验前的腿部瘦体重与<σ>_M1呈线性关系,即<σ>_M1随腿部瘦体重增加而增加;运...     

神经肌肉电刺激下小腿肌肉的电学特性研究

目的 采用电阻抗成像（electrical impedance tomography,EIT）方法研究神经肌肉电刺激（neuromuscular electrical stimulation,NMES）下小腿肌肉的电学特性,旨在将EIT作为一种长期监测方法,从而可视化NMES训练对人类小腿肌肉的训练效果。方法 16名实验对象被随机分配到对照组（control group,CG,n=8）和最佳电压强度的NMES训练组（optimal voltage intensity training group,OG,n=8）。对照组保持正常生活方式并不进行NMES和其他的肌肉训练;NMES训练组中使用商业NMES设备对实验对象右小腿进行23 min的NMES训练,每周3次,为期5周。应用EIT测量在每周一训练开始前的电导率分布。并且采用生物电阻抗分析（bioelectrical impedance analysis,BIA）方法测量右腿细胞外含水量与身体总含水量的比率（ECW/TBW） βrl,及身体总含水量（TBW）τ。为了量化NMES在肌肉训练过程中的作用,使用配对样本t检验分析EIT重建图像的...     

Influence of mechanical impedance on root exudation of maize seedlings at two development stages

Studies were undertaken to evaluate the effects of mechanical impedance on root exudation by maize (Zea mays L., var Dea) and to examine the importance of these effects in relation to the stage of plant development. Plants were grown under sterile and hydroponic conditions. Mechanical impedance was simulated using glass beads of 1 mm diameter. This treatment was compared with a control without beads. Results demonstrated that plant growth was influenced by mechanical impedance. Mechanical impedance markedly affected the growth of the shoot, whether this was measured as leaf area or total dry matter. Besides increasing root/shoot biomass ratios, mechanical impedances also stimulated root exudation of organic and inorganic compounds. Stressed plants lost more nitrogenous compounds than control plants. Otherwise, the percentage of released carbon decreased. Depending on the developmental stage of the plant, there was a large variation in the magnitude and time course on mechanical impedance effects. The effects of mechanical impedance persist and accentuate with time.     

Matching models of left ventricle and systemic artery

To reveal how the matching models of the left ventricle and its afterload affect the pressure and flow in the aortic root, the differences between the measured pressure and flow waveforms and those determined by three kinds of matching model were compared. The results showed that, compared with the results by both matching models 1 and 2, the pressure and flow waveforms determined by matching model 3 established in this work were in the closest agreement with the corresponding experimental waveforms, therefore indicating that matching model 3 was a matching model that closely and rationally characterized the match between the left ventricle and the systemic artery.