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81.
Chemical kinetic and diffusional limitations on bicarbonate reabsorption by the proximal tubule. 下载免费PDF全文
It is accepted that bicarbonate reabsorption in the proximal tubule is mediated by H+ secretion, but several aspects of this process have remained controversial. To examine some of these issues, we have developed a model that allows for spatial variations in the concentrations of CO2, HCO3-, and H2CO3 within the tubule lumen and cell cytoplasm, passive transport of these substances across cell membranes, carbonic anhydrase-catalyzed interconversion of HCO3- and CO2 within the cell and at the luminal membrane surface, and the corresponding uncatalyzed reactions in lumen and cell. Most of the required kinetic and transport parameters were estimated from physicochemical data in the literature, whereas intracellular pH and HCO3- permeability at the basal cell membrane, found to be the most significant parameters under normal conditions, were adjusted to yield reabsorption rates of "total CO2" (tCO2, the sum of CO2, HCO3- and H2CO3) comparable to measured values in the rat. Our results suggest that for normal carbonic anhydrase activity, almost all tCO2 leaves the lumen as CO2, yet the transepithelial differences in CO2 partial pressure does not exceed approximately 2 mm Hg. Electrochemical potential gradients favor substantial passive backleak of HCO3- from cell to lumen. Gradients in CO2 partial pressure remain small during simulated inhibition of carbonic anhydrase, with approximately 70% of tCO2 leaving the lumen as H2CO3 in this case, and the remainder as CO2. Predicted tCO2 reabsorption rates for carbonic anhydrase inhibition are approximately of normal, in good agreement with recent measurements in the rat, indicating that the concept of "carbonic acid recycling" is viable. 相似文献
82.
Louis G Chicoine Jose W Avitia Cody Deen Leif D Nelin Scott Earley Benjimen R Walker 《Journal of applied physiology》2002,93(1):311-318
Chronic hypoxia (CH) increases pulmonary endothelial nitric oxide synthase (eNOS) protein levels in adult rats but decreases eNOS protein levels in neonatal pigs. We hypothesized that this differing response to CH is due to developmental rather than species differences. Adult and neonatal rats were placed in either hypobaric hypoxia or normoxia for 2 wk. At that time, body weight, hematocrit, plasma nitrite/nitrate (NOx(-)), and right ventricular and total ventricular heart weights were measured. Percent pulmonary arterial wall area of 20-50 and 51-100 microm arteries were also determined. Total lung protein extracts were assayed for eNOS levels by using immunoblot analysis. Compared with their respective normoxic controls, both adult and neonatal hypoxic groups demonstrated significantly decreased body weight, elevated hematocrit, and elevated right ventricular-to-total ventricular weight ratios. Both adult and neonatal hypoxic groups also demonstrated significantly larger percent pulmonary arterial wall area compared with their respective normoxic controls. Hypoxic adult pulmonary eNOS protein and plasma NOx(-) were significantly greater than levels found in normoxic adults. In contrast, hypoxic neonatal pulmonary eNOS protein and plasma NOx(-) were significantly less compared with normoxic neonates. We conclude that there is a developmental difference in eNOS expression and nitric oxide production in response to CH. 相似文献
83.
Permselectivity of the glomerular capillary wall to macromolecules. II. Experimental studies in rats using neutral dextran. 总被引:8,自引:0,他引:8 下载免费PDF全文
R L Chang I F Ueki J L Troy W M Deen C R Robertson B M Brenner 《Biophysical journal》1975,15(9):887-906
To determine the permselectivity characteristics of the glomerular capillary wall, known molecular size fractions of [3H]dextran, prepared by gel chromatography, were infused into normally hydrated Wistar rats, thus permitting simultaneous measurement of Bowman's space/plasma water (BS/P) and urine/plasma water (U/P) concentration ratios, along with glomerular pressures and flows. Since (BS/P)inulin = 1.01 +/- 0.01 SE(n = 34, radius = approximately 14 A) and since (BS/P)dextran/(BS/P)inulin equaled (U/P)dextran/(U/P)inulin for dextrans ranging in molecular radius from 21 to 35 A, these findings validate that dextrans are neither secreted nor reabsorbed. For dextran radii of 20, 24, 28, 32, 36, 40, and 44 A, (U/P)dextran/(U/P)inulin averaged 0.99, 0.92, 0.69, 0.42, 0.19, 0.06, and 0.01, respectively. In accord with theoretical predictions that these fractional dextran clearances should vary appreciably with changes in glomerular transcapillary pressures and flows, an increase in glomerular plasma flow rate, induced in these same rats by plasma volume expansion, resulted in a highly significant lowering of fractional clearance of all but the smallest and largest dextrans studied. These findings emphasize that fractional solute clearances alone are inadequate to describe the permselective properties of the glomerular capillary wall unless glomerular pressures and flows are also known. This sensitivity of fractional dextran clearance to changes in plasma flow indicates that dextrans are transported across the capillary not only by bulk flow but also to an important extent by diffusion. 相似文献
84.
85.
Michelle Boone Ali Mobasheri Robert A. Fenton Bas W. M. van Balkom Ronnie Wismans Catharina E. E. M. van der Zee Peter M. T. Deen 《Journal of molecular histology》2010,41(1):61-74
Endocytosis, subsequent protein sorting into multivesicular bodies (MVBs), and eventual degradation in lysosomes compose an
important mechanism for controlling protein expression on the plasma membrane. The lysosomal trafficking regulator interacting
protein-5 (LIP5) is part of the complex protein machinery involved in MVB biosynthesis. LIP5 interacts with other players
of the ESCRT machinery as well as with two known cargo proteins, AQP2 and EGFR, whose degradation is affected upon reduction
of LIP5 expression. To investigate the expression and localization pattern of LIP5, we studied LIP5 protein expression in
a mouse tissue panel and subjected various rodent and human tissues to immunohistochemistry. Immunoblotting revealed that,
except for jejunum, LIP5 is expressed as a 42 kDa protein in all mouse tissues tested. Alternatively-spliced gene products
could not be detected. Immunohistochemical studies revealed that in tissues positive for LIP5, LIP5 is detected in virtually
all epithelial cells of the examined rodent and human tissues. The observed LIP5 expression in epithelial tissues suggests
that LIP5 is of particular importance in the MVB sorting and degradation of proteins expressed in polarized cells. 相似文献
86.
87.
Gynodioecy, the co-occurrence of female and hermaphroditic individuals within a
population, is an important intermediate in the evolution of separate sexes. The
first step, female maintenance, requires females to have higher seed fitness compared
with hermaphrodites. A common mechanism thought to increase relative female fitness
is inbreeding depression avoidance, the magnitude of which depends on hermaphroditic
selfing rates and the strength of inbreeding depression. Less well studied is the
effect of biparental inbreeding on female fitness. Biparental inbreeding can affect
relative female fitness only if its consequence or frequency differs between sexes,
which could occur if sex structure and genetic structure both occur within
populations. To determine whether inbreeding avoidance and/or biparental
inbreeding can account for female persistence in Geranium maculatum, we
measured selfing and biparental inbreeding rates in four populations and the spatial
genetic structure in six populations. Selfing rates of hermaphrodites were low and
did not differ significantly from zero in any population, leading to females gaining
at most a 1–14% increase in seed fitness from inbreeding avoidance.
Additionally, although significant spatial genetic structure was found in all
populations, biparental inbreeding rates were low and only differed between sexes in
one population, thereby having little influence on female fitness. A review of the
literature revealed few sexual differences in biparental inbreeding among other
gynodioecious species. Our results show that mating system differences may not fully
account for female maintenance in this species, suggesting other mechanisms may be
involved. 相似文献
88.
Ashik Jawahar Deen Kirsi Rilla Sanna Oikari Riikka K?rn? Genevieve Bart Jukka H?yrinen Avinash Rahul Bathina Antti Ropponen Katri Makkonen Raija H. Tammi Markku I. Tammi 《The Journal of biological chemistry》2014,289(12):8375-8389
Hyaluronan synthases (HAS1–3) are unique in that they are active only when located in the plasma membrane, where they extrude the growing hyaluronan (HA) directly into cell surface and extracellular space. Therefore, traffic of HAS to/from the plasma membrane is crucial for the synthesis of HA. In this study, we have identified Rab10 GTPase as the first protein known to be involved in the control of this traffic. Rab10 colocalized with HAS3 in intracellular vesicular structures and was co-immunoprecipitated with HAS3 from isolated endosomal vesicles. Rab10 silencing increased the plasma membrane residence of HAS3, resulting in a significant increase of HA secretion and an enlarged cell surface HA coat, whereas Rab10 overexpression suppressed HA synthesis. Rab10 silencing blocked the retrograde traffic of HAS3 from the plasma membrane to early endosomes. The cell surface HA coat impaired cell adhesion to type I collagen, as indicated by recovery of adhesion following hyaluronidase treatment. The data indicate a novel function for Rab10 in reducing cell surface HAS3, suppressing HA synthesis, and facilitating cell adhesion to type I collagen. These are processes important in tissue injury, inflammation, and malignant growth. 相似文献
89.
90.