Amount Of PO Research Articles

Distribution Characteristics of Soil Organic Phosphorus Fractions in the Inner Mongolia Steppe

Phosphorus (P) is one of the limiting nutrients in Inner Mongolia steppe soil, which seriously affect steppe productivity. Therefore, it is necessary to understand the distribution characteristics of organic P (Po) fractions and their influencing factors in Inner Mongolia steppe soil and to identify the contribution of Po fractions to soil available P (AP) to maintain the sustainable development of the Inner Mongolia steppe by improving the utilization rate of Po. The contents of soil Po fractions such as H2O-extractable Po (H2O-Po), NaHCO3-extractable Po (NaHCO3-Po), HCl-extractable Po (HCl-Po), NaOH-extractable Po (NaOH-Po), and phytate P (Phyt-P) were determined in soil samples (0–15 cm) from 15 sampling sites representing three types of grassland (i.e., desert steppe, typical steppe, and meadow steppe) in Inner Mongolia. The influencing factors of the soil Po fractions were determined by redundancy analysis (RDA). Soil Po content accounted for 61.0% of the total P (TP) on average. NaOH-Po was the main fraction of Po, accounting for 49.1% of Po on average; H2O-Po content accounted for the least amount of Po (mean 1.3 mg kg−1). H2O-Po and HCl-Po were not significantly different among the three steppes. The contents of NaHCO3-Po increased in the order of desert steppe < typical steppe < meadow steppe, and the trend of NaOH-Po and Phyt-P contents were desert steppe < meadow steppe < typical steppe. Pearson correlation analysis showed that NaHCO3-Po was positively correlated with AP (r = 0.86, p < 0.01). HCl-Po was negatively correlated with AP (r = − 0.56, p < 0.05). NaOH-Po and Phyt-P were significantly positively correlated with NaHCO3-extractable inorganic P (NaHCO3-Pi); Phyt-P was also negatively correlated with HCl-extractable Pi (HCl-Pi) (r = − 0.61, p < 0.05). These correlations were mainly caused by differences in steppe types and soil properties caused by climatic conditions, as shown by the result of RDA analysis. Soil Po plays an indispensable role in the supply of soil P in the semi-arid steppe of Inner Mongolia, where NaHCO3-Po and HCl-Po strongly contributed to AP. In addition, NaOH-Po and Phyt-P as a part of stable pools are important for providing P to other P pools. Po fractions in steppe soils were mainly regulated by climatic conditions and are closely related to the soil organic matter and pH.

Rousing the dragon: Polonium production for neutron generators in the Manhattan Project

During the Manhattan Project, the rare element polonium (Po) was synthesized by neutron bombardment of bismuth in nuclear reactors for use in neutron-generating triggers that were used to initiate the fission chain reactions in the Hiroshima and Nagasaki bombs. In this paper, I explore the physics of why polonium was used, why the triggers contained the amount of polonium that they did, and for how long a given mass of bismuth had to be irradiated in the Oak Ridge X-10 pile or a Hanford plutonium-production pile to generate a given amount of Po. A simple neutron-flux model gives results in reasonable accord with estimates recorded in a 1943 letter written by Robert Oppenheimer.

Effects of light fraction organic matter removal on phosphate adsorption by lake sediments

Abstract The adsorption of PO 4 3 - on lake sediments has an important influence on the transport, degradation, and ultimate fate of P in lake ecosystems. Organic matter in sediment strongly affects PO 4 3 - adsorption, with light fraction organic matter (LFOM), the labile fractions representing only a small proportion of the total organic matter, playing a key role in nutrient cycling in lakes. However, little is known about the effect of LFOM on PO 4 3 - adsorption by sediments. This study examined the effects of LFOM removal on PO 4 3 - adsorption by lake sediments with different trophic status. Results showed that the removal of LFOM did not significantly affect PO 4 3 - adsorption kinetics, which was greatest during the first 0.5 h and reached an equilibrium state thereafter. The amount of PO 4 3 - adsorbed decreased due to LFOM removal from the sediments, especially in the first 0.5 h. The PO 4 3 - adsorption rates for the sediments from Gonghu Lake, Wuli Lake and Yuehu lake decreased from 302.44 mg (kg h) −1 to 138.93 mg (kg h) −1 , 322.88 mg (kg h) −1 to 149.21 mg (kg h) −1 and 415.36 mg (kg h) −1 to 46.77 mg (kg h) −1 , respectively. The removal of LFOM accelerated PO 4 3 - release from sediments to the overlying water, and PO 4 3 - adsorption efficiency decreased by 83.75%, 70.90% and 66.75% for Gonghu Lake, Wuli Lake and Yuehu Lake, respectively. Two plausible explanations contributed to the decrease, one was the replacement of PO 4 3 - which was in the form of Fe/Al-bound P in the sediment by OH due to the increased pH, and the other is the destruction of LFOM colloids by the carboxyl group ( COOH) and hydroxyl (–OH).

Changes in Bone Quality Associated with the Mineralization of New Bone Formed Around Implants - Using XPS, Polarized Microscopy, and FTIR imaging -

The purpose of this study was to investigate changes in bone quality associated with the mineralization of new bone forming around implants. Eight 18-week-old male New Zealand white rabbits and implants fabricated from Ti-15%Zr-4%Nb-4%Ta alloy were used in the study. Characteristics of new bone formed around implants at 4 and 8 weeks and cortical bone were compared using X-ray photoelectron spectroscopy (XPS) for elemental qualitative and quantitative analysis, polarized microscopy (PM) for histological examination, and Fourier transform infrared Imaging (FTIR Imaging) to characterize molecular distributions in new bone and cortical bone. Results from XPS analysis showed changes in the chemical bonding in new bone over time (4 weeks vs. 8 weeks). PM showed changes in collagen birefringence, orientation and intensity in new bone over time, becoming more similar to those of cortical bone after 8 weeks. FTIR Imaging showed that in new bone close to cortical bone, amounts of PO 4 3- and CO 3 2- ions (representing mineral or inorganic components), and amounts of amide I (representing the organic component) increased over time as mineralization progressed. In new bone more distant from cortical bone, PO 4 3- , CO 3 2- , and amide I distributions also increased over time, but to a lesser extent to that observed near cortical bone. Our findings clearly showed changes in the quality of new bone forming around implants, and these changes were related to mineralization.

Ion Releasing Abilities of Phosphate Invert Glasses Containing MgO, CaO or SrO in Tris Buffer Solution

CaO-TiO2-P2O5-Na2O invert glasses developed in our group showed bioactivity and good sinterability. In the present work, phosphate invert glasses, in which CaO was substituted with MgO or SrO (PIG-MO, M = Mg, Ca, Sr), were prepared and their ion-releasing behaviors were evaluated. Glass transition temperature (Tg) and crystallization temperature (Tc) were estimated from differential thermal analysis. (Tc – Tg)/Tg value, which indicates glassification of the glass, of PIG-MgO was higher in comparison with those of the other glasses. Laser Raman spectroscopic analysis indicated that peaks due to P2O7 4– group in the spectrum of PIG-MgO were smaller than those in the spectra of PIG-CaO and PIG-SrO. The structure of PO4 3–-M2+PO4 3– was expected to form easily, resulting in the good glassification of PIG-MgO. The ion amounts dissolved from PIG-MgO containing a large amount of PO4 3– group were 2 ∼ 3 times larger than those of the other glasses.

LEACHING AND SORPTION OF NITROGEN AND PHOSPHORUS BY CROP RESIDUE

Overland flow from cropland areas often contains nutrients and residue materials can either contribute to runoffnutrient load through leaching or remove nutrients by sorption. Measurements were made of leaching and sorption of nitrogenand phosphorus from corn (Zea mays L.), soybean (Glycine max (L.) Merr.) and winter wheat (Triticum aestivum L. cv.Pastiche) residues placed in solutions containing inorganic nutrients. Variables used were type of residue material, nutrientconstituent, solution concentration, and residue / solution contact time. For a given residue material and nutrient constituent,four different solution concentrations were used (PO4 -P: 0 to 16 .g mL-1; NO3 -N and NH4 -N: 0 to 24 .g mL-1), and changesin solution concentration over five selected residue / solution contact times (25 to 86400 sec) were measured. Soybean andwheat residue contained relatively small amounts of NO3 -N and therefore had minimal impact on the NO3 -N content of thesolutions. An increase in initial solution concentration did not substantially affect PO4 -P leaching from corn and soybeanresidue but caused the amount of NH4 -N removed to decrease. As residue solution / contact time increased from 25 to 86400 s(1 day), the amount of PO4 -P leached from corn and soybean residue consistently increased. Wheat residue sorbed PO4-Pwith an increase in sorption generally resulting from greater residue solution / contact time. Thus, crop residue materialsappear to have the potential to influence the N and P content of runoff through leaching and sorption.

Enzymatic hydrolysis of organic phosphorus in extracts and resuspensions of swine manure and cattle manure

Animal manure can be a valuable resource of P for plant growth. Organic phosphates (Po) are considered bioavailable if they can be hydrolyzed to inorganic P (Pi). Therefore, investigation of the susceptibility of manure Po to hydrolysis may increase our understanding of manure Po bioavailability. In this study, we demonstrate that three orthophosphate-releasing enzymes, acid phosphatase from wheat germ, alkaline phosphatase from bovine intestinal mucosa, and fungal phytase from Aspergillus ficcum, were able to hydrolyze certain amounts of Po in animal manure. A scheme of sequential enzymatic release of Po in manure was developed and then used to investigate changes in swine and cattle manure P distribution after storage at −20°C, 4°C or 22°C for about a year. Assuming that the P distribution in manure maintained at −20°C remained unchanged (i.e., similar to fresh manure), bioavailable P (Pi and enzyme-hydrolysable Po) in swine manure remained relatively constant [72.8–76.3% of total P (Pt)]. Soluble but enzymatically unhydrolysable Po (Pue) increased from 7.2% to 32.1% of Pt during storage at 4°C. In cattle manure, bioavailable P decreased from 71.6% to 62.9% of Pt, and Pue increased from 21.7% to 37.2% of Pt during storage at 22°C. These data indicated that the major change during the storage of animal manure for a year was the increase in Pue, so manure P solubility may increase with storage, but the increase would not produce more bioavailable P in the manure. The effects of storage on the bioavailability of manure P should be further investigated to develop an efficient manure-P management strategy.

Phosphorus pools in Oxisols under shaded and unshaded coffee systems on farmers' fields in Brazil

Phosphorus (P) is a primary limiting nutrient for crop production in weathered tropical soils. The deficiency is mainly caused by sorption of phosphate onto Al- and Fe- (hydr)oxides. We hypothesise that the distribution of soil P among various pools is influenced by land use. Our objective was to characterise the soil inorganic (Pi) and organic P (Po) pools and to compare the various pools at different depths in agroforestry (shaded) and monocultural (unshaded) coffee cultivation systems. The study was carried out in the Atlantic Coastal Rainforest domain, Brazil, with Oxisols as the dominant soil type. Soils were collected from four farmers' coffee (Coffea arabica L.) fields, two agroforestry and two monocultural systems. Three profiles were sampled per field, at depths of 2–3, 10–15 and 40–60 cm. A simplified sequential P fractionation was carried out, using resin, 0.5 M NaHCO3, 0.1 M NaOH, 1 M HCl and concentrated HCl as extractants. Sum-P (resin, NaHCO3 NaOH, 1 M HCl and concentrated HCl) ranged from 370 to 830 mg kg−1. Concentrated HCl extracted the largest portion (74%), followed by NaOH (22.5%). Labile (sum of resin, NaHCO3 and NaOH) P ranged from 13 to 40% of Sum-P. The major part (62%) of the labile fraction was Po. In the agroforestry fields, the amount of Po decreased less with depth and the percentage of Po in labile pools was higher than in monocultural fields. This suggests that agroforestry maintains larger fractions of P available to agricultural crops by influencing the dynamics of P through the conversion of part of the Pi into Po, thereby reducing P losses to the unavailable pools.

DETERMINATION OF TOTAL AND DISSOLVED PHOSPHORUS IN AGRICULTURAL RUNOFF SAMPLES BY INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRY

Leaching of nutrients to the drainage network is an important factor in polluting surface waters, with Phosphorus (P) often being the element of concern. Because P is strongly bound to sediments, different P fractions, including total, particulate and total dissolved P are now routinely measured. For the traditional determination of total P, a digestion followed by UV–Vis detection procedure was applied. The “true” total P content resulted from the digestion of a raw water sample containing suspended matter. Whereas the digestion performed to the sample after filtration through 0.45 μm membrane filter, gave the total dissolved P. The goal of this study was to measure the different fractions of P by ICP-MS. In the case of total P, no addition of coloring agents was necessary after the digestion process. Dissolved P was measured directly after filtration, without the previous digestion and no manipulation of the sample. Similar results were obtained by UV–Vis and by ICP-MS when measurements of demi water spiked with two different amounts of PO4 −3 were performed. Various agricultural runoff samples were digested with (NH4)2S2O8+H2SO4 30% (v/v) for total P determination. Again, similar results were obtained for both techniques. Three certified water samples from the Canadian National Water Research Institute were analyzed for dissolved P by ICP-MS. Beryllium and Sc were added as internal standards for possible drift corrections. Detection limits of 5 μg L−1 and linearity ranges from 10 μg L−1 to 5 mg L−1 were achieved.

Analysis of phosphorus by 31PNMR in Oxisols under agroforestry and conventional coffee systems in Brazil

Phosphorus (P) is the primary limiting nutrient for crop production in highly weathered tropical soils. The deficiency is mainly caused by strong adsorption of H 2PO 4 − to Al- and Fe-(hydr)oxides, which turns large proportions of total P into a form that is unavailable to plants. Soil management modifies P dynamics. Some plants, including trees used in agroforestry systems, are known to accelerate P cycling. The objective of this paper was to use phosphorus 31 nuclear magnetic resonance ( 31PNMR) to evaluate the inorganic (Pi) and organic P (Po) compounds in Oxisol from two agroforestry (15 and 19 years old) and two conventional (full-sun, monoculture, ca. 15–20 and 20–24 years) coffee systems at three different depths (2–3, 10–15 and 40–60 cm). We hypothesised that the amounts of (1) organic P and (2) diester are higher in agroforestry fields than in conventional coffee fields and (3) the organic P and the diester decrease less with depth in the agroforestry systems than in the conventional systems. The soils were sampled from on-farm experiments in the Atlantic Coastal Rainforest, Brazil. The soil P was extracted with NaOH 0.5 M+EDTA 0.1 M. Resin chelex-X100 was used to remove the paramagnetic ions. The total P in the NaOH–EDTA extract was measured through ICP and the Pi by the ammonium molybdate–ascorbic acid method. Po was calculated as the difference between total P and Pi. The amount of Po was higher, the decrease of Po with depth was more sharp and the Po/total P was lower in the conventional systems than in the agroforestry systems. Based on literature and standards, 31PNMR signals were interpreted as inorganic orthophosphate, orthophosphate monoester (inositol phosphates and mononucleotides), orthophosphate diester (phospholipids, nucleic acids and teichoic acid) and pyrophosphates. The proportion of organic P (Po) was on average 47%, consisting of monoester (95%) and diester (5%). The amounts of diester phosphates did not differ between systems, but the proportion of diester to total spectra areas was higher and the decrease of diester with depth was less in the agroforestry than in the conventional systems. The proportions of inorganic P to total P consisted on average of 45% orthophosphate and 8% pyrophosphate. Our results suggest that agroforestry systems influence the dynamics of P through the conversion of part of the inorganic P into organic P. The effect was higher in deeper layers. Because the rate of cycling is higher for organic P than for inorganic P and for diester than for monoester, and because the P in deep layers is normally less available to crop plants, agroforestry would maintain larger fractions of P available to agricultural crops, thereby reducing P losses to the unavailable pools. The rate and the impacts of these changes on P cycling and efficiency of P use of the crops in the long-term need to be further examined and understood, for full evaluation of the importance of agroforestry in soil P utilisation.

Root-induced modifications of the exchange of phosphate ion between soil solution and soil solid phase

The uptake of phosphorus (P) by roots results in a depletion of phosphate ions (PO4) in the rhizosphere. The corresponding decrease in PO4 concentration in the soil solution (CP) gives rise to a replenishment of P from the solid phase which is time- and CP-dependent. This PO4 exchange which reflects the buffer power of the soil for PO4 also varies with the composition and the physico-chemical conditions of the soil. As root activity can modify these physico-chemical conditions in the rhizosphere, the question arises whether these modifications affect the ability of PO4 bound to the soil solid phase to exchange with PO4 in soil solution. The aim of the present work was to measure and compare the parameters which describe the amount of PO4 bound to soil solid phase that is capable to replenish solution P for both rhizosphere and bulk soils. The soil sample was a P-enriched, calcareous topsoil collected from a long-term fertiliser trial. Rhizosphere soil samples were obtained by growing dense mats of roots at the surface of 3 mm thick soil layer for one week. Three plant species were compared: oilseed rape (Brassica napus L., cv Goeland) pea (Pisum sativum L., cv. Solara) and maize ( Zea mays L., cv. Volga). The time- and CP-dependence of the PO4 exchange from soil to solution were described using an isotopic dilution method. The measured CP values were 0.165 mg P L−1 for bulk soil and 0.111, 0.101 and 0.081 mg P L−1 for rhizosphere soils of maize, pea and rape, respectively. The kinetics of the PO4 exchange between liquid and solid phases of soil were significantly different between rhizosphere and bulk soils. However, when changes in CP were accounted for, the parameters describing the PO4 exchange with time and CP between soil solution and soil solid phase were found to be very close for bulk and rhizosphere soils. For this calcareous and P-enriched soil, plant species differed in their ability to deplete PO4 in solution. The resulting changes in the ability of the soil solid phase to replenish solution PO4 were almost fully explained by the depletion of soil solution P.

Reactive Fe controls the relative amount of PO4 extracted from acidic soils by NaHCO3 and by acidic fluoride I. Soils without recent P additions

The relations of reactive Fe and Al fractions (oxalate-extractable) with 2 measures of extractable orthophosphate (Colwell and Bray-1) were examined for 47 acidic, mineral, surface soils from eastern New South Wales. The soils had developed from 3 different parent materials and had a wide range of chemical compositions; most would have been P-deficient in their virgin state. Some of the soils had received P fertiliser to promote pasture growth but none had been fertilised with P for at least 2 years before sampling. Variation among soils in the log of the ratio of values for the P tests (Colwell/Bray-1) was related to the log of the concentration of either oxalate Fe (R2 = 0 · 87) or oxalate Al (r2 = 0 · 24), or P sorption (r2 = 0 · 26). Soil parent material had no significant effect on these relations. Two independent data sets support the strong relation of log (Colwell/Bray-1) with log(oxalate Fe); however, not all of the relations are identical and possible reasons for the differences are discussed. The complete set of relations indicates that under the described conditions, much of the orthophosphate may be bound to reactive Fe. It is inferred that across a set of acidic, mineral soils that have not had recent additions of P and which vary widely in Feox, the critical levels of the Colwell test should vary over a much wider range than the corresponding Bray-1 values. Consequently, for the Colwell test to provide as reliable a guide to P responses as the Bray-1 test, the Colwell test should be used in conjunction with a measure of reactive Fe, such as oxalate-extractable Fe.

The phosphatidylinositol-glycolipid anchor on alkaline phosphatase facilitates mineralization initiation in vitro.

Alkaline phosphatase (AP) is required for the proper mineralization of cartilage and bone. The enzyme is localized to the outer surface of cells through a phosphatidylinositol-glycolipid anchor, which is covalently attached to the carboxyl terminus of the protein. In calcifying cartilage, AP-rich matrix vesicles (MVs) are released into the matrix from chondrocytes, and apatite formation is initiated within and around these particles. In this paper we examine the role of the AP glycolipid anchor using an in vitro mineralization assay system. AP was purified to homogeneity, and the purified enzyme was used to drive mineral formation in vitro with and without the anchor. Mineral formation was initiated through phosphate release from beta-glycerol phosphate (beta-GP). The amount of PO4(-3) released was similar whether the anchor was present or absent. However, SEM and X-ray microanalysis revealed that the mineral produced by anchored AP was indistinguishable from that produced by MVs and that both of those minerals were more apatite-like than mineral formed by soluble AP or through spontaneous precipitation. Taken together, the data suggest that in addition to providing PO4(-3) to drive mineralization, AP influences the nature of the mineral formed. Further, AP containing its glycolipid anchor produces mineral comparable with that formed by tissue-derived MVs. Thus, in the absence of extracellular matrix, MV mineralization in vitro can be emulated by glycolipid-anchor containing AP.

The nature of humic acid‐apatite interaction products and their availability to plant growth

Abstract An investigation was conducted to determine the nature of decomposition products resulting from the interaction between humic acid and apatite and assess their availability to plant growth. Interaction analyses were performed by shaking 200 mg apatite with 0 to 800 mg/L HA or FA solutions at pH 5 or 7 for 0 to 12 hr. Phosphorus concentrations were determined in the supernatants by spectrophotometry. The nature of P‐humic acid complexes was determined by 31P NMR analysis. Availability of these dissolution products was studied by growing corn plants in aerated hydroponics to which 200 mg apatite and 0 to 800 mg/L HA were added at pH 5 or 7. The results indicated that the rate of dissolution of apatite was parabolic in regression with time, and increased by increasing the amounts of HA or FA applied from 100 to 800 mg/L The dissolution reaction was influenced by pH, because larger amounts of PO4 3‐ions were detected at pH 5 than at pH 7. 31P NMR spectroscopy indicated the presence of P‐humic acid co...

Phosphorylation and dephosphorylation of the insulin receptor: evidence against an intrinsic phosphatase activity.

We have studied the reversibility of insulin receptor phosphorylation to establish the relation between this autophosphorylation reaction and the initiation of insulin action and between dephosphorylation and the termination of insulin effects in cells. In cultured Fao hepatoma cells labeled with 32PO4(3-), insulin increased 5-fold the phosphorylation of the beta-subunit of the insulin receptor at serine, threonine, and tyrosine residues. Addition of anti-insulin antiserum to cells incubated with insulin caused dissociation of insulin from the receptor and concurrent dephosphorylation of the beta-subunit. 32PO4(3-) associated with the insulin-stimulated receptor could be decreased by the addition of sodium phosphate to the medium but with a slower time course. Insulin stimulated phosphorylation of insulin receptor purified partially on immobilized wheat germ agglutinin. This reaction utilized [gamma-32P] ATP and occurred exclusively on tyrosine residues. Addition of unlabeled ATP caused a decrease in the amount of PO4(3-) associated with the receptor. Insulin-stimulated phosphorylation was also observed if the receptors were further purified by immunoprecipitation with anti-insulin receptor antibody prior to the phosphorylation reaction; however, addition of unlabeled ATP to this system did not chase the labeled 32PO4(3-) from the beta-subunit. These data are consistent with the notion that phosphorylation and dephosphorylation of the insulin receptor parallel the onset and termination of insulin action. Phosphatase activity involved in the dephosphorylation of the insulin receptor appears to be a glycoprotein because it was retained after partial purification of the receptor on wheat germ agglutinin-agarose; however, this phosphatase activity is distinct from the insulin receptor because it was not retained after immunoprecipitation of the receptor with anti-insulin receptor antibodies.

Adsorption of benzenecarboxylic acids onto hydroxyapatite and human enamel powder

Isotherms were obtained for the adsorption of benzenehexacarboxylic acid (HexA) and benzene1,3,5-tricarboxylic acid (TriA), as well as for the corresponding sodium salts (HexNa and TriNa), onto synthetic hydroxyapatite crystals (HA) or enamel powder (EP). The studies were also performed as a function of pH and in the presence of various amounts of PO 4 −3 ions. Different results were obtained when studying adsorption of benzenepolycarboxylic acids or their corresponding salts and when treating EP or HA. The fact that the amounts of HexA or HexNa taken up by either HA or EP were 7 to 10 times greater than those of TriA is particularly important. Taking into account specific surface areas and the maximum molecular surfaces of HexA and TriA, an adsorption shell was formed in the case of EP which is 8 times thicker than that on HA. Adsorption versus pH appears to be maximum at pH 5, whereas the presence of phosphate ions increased uptake of HexNa and TriNa and decreased adsorption of HexA and TriA. A Langmuir-type adsorption model fitted the experimental results for low concentrations. The facts that affinities for HexA were higher than those for HexNa and that N parameters for HexA were four times greater for EP than for HA were also significant.

PO4 transport in superficial and juxtamedullary nephrons in the cat: evidence for nephron heterogeneity.

Many micropuncture studies have demonstrated a difference between the delivery of PO4 from late superficial distal convoluted tubules and final urinary PO4 excretion. This difference could be due to PO4 transport in nephron segments beyond the late distal tubule (1) or to differing transport rates in deep nephrons (2). The latter possibility would suggest that lesser amounts of PO4 delivered from deep nephrons combined with the PO4 delivered from superficial nephrons and the algebraic sum is the final urinary PO4 content. To study the role of deep nephrons in PO4 transport with particular reference to the quantitative contribution of deep and superficial nephrons, micropuncture and A-V extraction studies were performed in the cat kidney. The cat is useful as a model for the study of nephron heterogeneity of transport since the superficial and juxtamedullary cortex are drained by discrete and accessible venous drainage systems (3).