Differential sensitivity of organic anion transporters in rat renal brush-border membrane to diethyl pyrocarbonate

The effect of various chemical modifiers on p-aminohippurate (PAH) uptake by a potential-sensitive system and by an anion exchanger was studied in rat renal brush-border membrane vesicles. Among various chemical modifiers, diethyl pyrocarbonate (DEPC) selectively inhibited potential-sensitive PAH uptake but not the uptake by the anion exchanger. The inhibitory effect of DEPC on potential-sensitive PAH uptake was not due to the facilitated dissipation of membrane potential, which was evidenced by the studies with a potential-sensitive fluorescence dye diS-C3(5). The potential-sensitive PAH uptake was inhibited by DEPC in a concentration-dependent manner, and kinetic analysis showed that the decreased uptake of PAH in DEPC-treated vesicles was due to the decrease of Vmax. The inhibition of the PAH uptake was protected by the presence of organic anions during the DEPC treatment. These findings indicate that PAH transport by the potential-sensitive system and by the anion exchanger is mediated by structurally distinct transporters. Amino acid residue(s) modified by DEPC, most likely a histidine residue, should play an important role in the potential-sensitive transport of PAH in rat renal brush-border membrane.

Cation-dependent gating of the hyperpolarization-activated cation current in the rabbit sino-atrial node cells

1. The gating properties of the hyperpolarization-activated cation current (I(f) or Ih) were investigated in single pacemaker cells dissociated from the rabbit sino-atrial node. 2. The whole-cell I(f) was recorded in the presence of different external cations. The inward I(f) was increased when external Na+ was replaced with K+, and was decreased in Li+ or Rb+ solution. In Tris+ and Cs+ solutions, the inward I(f) was negligible. The outward tail current recorded upon depolarization was largest in Li+ solution and smaller in a sequence of Na+, Tris+ and K+ solutions. In Rb+ and Cs+ solutions, only a small tail current was recorded. 3. The outward tail current had a 'shoulder' in Na+ solution, which was much delayed by replacing Na+ with Li+. In K+ solution, the decay of the tail current was much faster, and no obvious shoulder was recorded. The tail current was slowest in Li(+)-rich and 0 mM K+ solution, and was progressively accelerated by adding K+ over the range from 0 to 3 mM. The tail current at 30 mM [K+]o showed only a small shoulder. A common binding site to modulate the I(f) deactivation was suggested for monovalent cations. 4. The shoulder of the I(f) tail became more evident as I(f) was activated to a larger extent either by prolonging the duration or by increasing the amplitude of the preceding hyperpolarization in both Na+ and Li+ solutions. 5. The I(f) was first activated by hyperpolarizing the membrane to -110 mV, and then deactivated by depolarization. The inward tail current at -50 mV showed a single exponential decay. At more positive potentials, the shoulder of the outward tail currents became more evident and the rate of the final decay was increased. 6. The time course of I(f) activation was well fitted with the sum of two exponential functions. Time constants of both components were not affected by the external cation (Na+, K+ or Li+) replacement. Likewise, the quasi-steady state activation was conserved when external Na+ was replaced with Li+. 7. Two closed and three open states were assumed in a sequential state model of the I(f) channel. The cation effects were well simulated by assuming that the deactivation rate was selectively modulated. The flow of I(f) during the spontaneous action potential was calculated. The activation of I(f) started on repolarization to the maximum diastolic potential and reached a maximum in the middle of the diastolic period. Its peak amplitude was 14% of the net inward current during the diastolic period.

[Simultaneous determination of catecholamines, serotonin, and their precursors and metabolites in body fluid by an HPLC system with multi-electrode electrochemical detector]

We have developed two HPLC systems for the simultaneous determination of CA, 5-HT and their precursors and metabolites in human body fluid. One system consisted of two reversed-phase columns, a column switching device, a pair of electrodes for elimination of interferents and two sets of new electrochemical detectors with four electrodes. Using this system, adequate separation of peaks for 17 kinds of CA, 5-HT and their related metabolites in a standard solution required only 17 min. NE, MHPG, DOPAC, 5-HIAA, HVA and TRP levels in cerebrospinal fluid (CSF) were determined without any pretreatment of the CSF samples. The concentrations of DOPAC, 5-HIAA and HVA in CSF were significantly lower in Alzheimer's disease, vascular dementia and Parkinson's disease than in the controls. The other system was developed for determination of CA acidic metabolites and 5-HIAA in human urine. This system consisted of a mixed-mode column (C18/anion) and 8-channel electrochemical detector with isocratic elution of citrate buffer. Detection limits, precision and analytical recoveries of this method were satisfactory for clinical use.

p-Aminohippurate transport in apical and basolateral membranes of the OK kidney epithelial cells

p-Aminohippurate (PAH) transport in apical and basolateral membranes of OK cells was studied to characterize each membrane process and to determine which process is important for the vectorial transport of PAH across the OK cell monolayers. PAH uptake from the basal side into OK cells was much higher than from the apical side, and was inhibited almost completely by anion transport inhibitors (probenecid and furosemide) and low temperature. On the other hand, PAH efflux from OK cells to the apical side was higher than to the basal side. The efflux across the apical membrane also was inhibited by the transport inhibitors and low temperature. The uptake of PAH across the basolateral membrane was inhibited by dicarboxylates such as alpha-ketoglutarate, and kinetic analysis showed that the inhibition was a mixed-type. These findings suggest that PAH transport in apical and basolateral membranes of OK cells is a specifically mediated process, and both processes contribute to the vectorial transport of PAH across the cell monolayers. PAH/dicarboxylate exchange may be involved in PAH transport in the basolateral membrane of OK cells.

Molecular evolution of shark C-type natriuretic peptides

C-type natriuretic peptides (CNP) of varying length were isolated from the atrium or ventricle of a shark, Lamna ditropis and their amino acid sequences were determined. Although the sequence of Lamna CNP was highly homologous to those of other CNPs sequenced to date, the Lamna CNP-41, the longest CNP identified in this study, has one amino acid replacement from those of Triakis scyllia and Scyliorhinus canicula, and three amino acid replacements from that of Squalus acanthias. The degree of similarity of CNP molecules coincides well with their systematic positions in the cladogram of elasmobranchs; Lamna, Triakis and Scyliorhinus belong to the same order, but Lamna and Squalus belong to different orders. The facts that Lamna and Triakis are in different suborders but Triakis and Scyliorhinus are in the same suborder and have identical CNP-41, also support this evolutionary implication.

Structure of the genomic DNA encoding cucumber ascorbate oxidase and its expression in transgenic plants

Genomic DNA (Aso1) encoding the ascorbate oxidase (ASO) of cucumber (Cucumis sativas) was cloned and sequenced. From a comparison of the sequences of Aso1 and its cDNA [Ohkawa et al. Proc. Natl. Acad. Sci. USA 86 (1989) 1239-1243], it was concluded that Aso1 consisted of four exons and three introns. In the 5'-flanking region, sequence motif resembling a TATA box and a CAAT box, were found 124 and 218 bp upstream, respectively, from the start codon. Sites of initiation of transcription, determined by primer extension, were the A and G residues located 90 and 93 bp, respectively, upstream from the initiation codon. ASO was abundant in cucumber fruits and stems. The 5'-flanking region, placed upstream of the structural gene of β-glucuronidase (GUS), expressed the GUS activity in cucumber plants in a transient expression assay after introduction of DNA with a particle gun. High-level GUS expression was found in stems of transgenic tobacco plants harboring Aso1 promoter-GUS chimeric gene.

Cellular toxicity of aminoglycoside antibiotics in G418-sensitive and -resistant LLC-PK1 cells

The effects of gentamicin and G418 on the cellular function of LLC-PK1 epithelial pig kidney cells were investigated. Exposing the cells for 2 days to these aminoglycoside antibiotics inhibited the increase in cell-associated apical membrane enzyme activity (alkaline phosphatase, aminopeptidase, and gamma-glutamyltransferase). Kinetic analysis revealed that the maximal activity of alkaline phosphatase was reduced by these aminoglycosides. Both aminoglycosides inhibited [3H]leucine incorporation into microsomes prepared from LLC-PK1 cells. The LLC-PK1 cells transfected with DNA encoding aminoglycoside 3'-phosphotransferase II, designated T2000B, were resistant to G418 as assessed by colony formation assay and the number of floating dead cells and by assay of apical enzyme activity. After a 4-hr exposure to G418, [3H]leucine incorporation in the host LLC-PK1 cells was inhibited, whereas that in T2000B cells was relatively unaffected. Gentamicin inhibited [3H]leucine incorporation similarly in both cells. The inhibition of protein synthesis by aminoglycosides occurred earlier than that of apical enzyme activity. These findings suggest that the inhibition of protein synthesis by aminoglycoside antibiotics is a possible cause of the reduction in cell viability as well as the apical enzymes in LLC-PK1 cells.

Sexual dimorphism of urine angiotensinogen excretion in the rat

To determine the source of angiotensinogen excreted in urine, urine angiotensinogen was measured in male and female rats during growth. Angiotensinogen in 24-hr urine, measured by direct radioimmunoassay with antibody against rat angiotensinogen, increased fourfold in males between the ages of 5 and 7 weeks, whereas no significant changes were observed in females or castrated males. Plasma levels of angiotensinogen, in contrast, showed no significant differences between these groups at any age. Castration of adult males caused a significant reduction of urinary angiotensinogen after 4 weeks. Consecutive s.c. administration of 17 alpha-methyltestosterone for 3 weeks in castrated males resulted in a threefold increase in the urinary excretion of angiotensinogen, as well as a twofold increase in the renal expression of angiotensinogen messenger RNA (mRNA). Renal levels of angiotensinogen mRNA in intact adult males were about threefold higher than those in females and castrated males, whereas there were no significant differences in hepatic angiotensinogen mRNA between these animals. These results suggest that the sexual differences in the urinary excretion of angiotensinogen are primarily due to the androgen-dependent dimorphic expression of angiotensinogen mRNA in the kidney; thus, levels of angiotensinogen in urine might reflect intrarenal production.

Bestatin transport in rabbit intestinal brush-border membrane vesicles

The effect of papain treatment on bestatin uptake by rabbit intestinal brush-border membrane vesicles (BBMVs) was studied. Papain treatment of BBMVs effectively diminished aminopeptidase activity but not bestatin uptake by a H+/dipeptide cotransporter. Bestatin uptake by BBMVs was composed of two saturable components, and after papain treatment the high-affinity component disappeared while the low-affinity component was retained. These findings suggest that high- and low-affinity components represent bestatin binding to aminopeptidase and the true uptake by the H+/dipeptide cotransporter, respectively.

Effects of intracellular pH on ATP-sensitive K+ channels in mouse pancreatic beta-cells

1. The effects of intracellular pH (pHi) on the ATP-sensitive K+ channel (K+ATP channel) from mouse pancreatic beta-cells were examined in inside-out patches exposed to symmetrical 140 mM K+ solutions. 2. The relationship between channel activity and pHi was described by the Hill equation with half-maximal inhibition (Ki) at pHi 6.25 and a Hill coefficient of 3.7. 3. Following exposure to pHi < 6.8, channel activity did not recover to its original level. Subsequent application of trypsin to the intracellular membrane surface restored channel activity to its initial level or above. 4. At -60 mV the relationship between pHi and the single-channel current amplitude was described by a modified Hill equation with a Hill coefficient of 2.1, half-maximal inhibition at pHi 6.48 and a maximum inhibition of 18.5%. 5. A decrease in pHi reduced the extent of channel inhibition by ATP: Ki was 18 microM at pH 7.2 and 33 microM at pH 6.4. The Hill coefficient was also reduced, being 1.65 at pH 7.2 and 1.17 at pH 6.4. 6. When channel activity was plotted as a function of ATP4- (rather than total ATP) there was no effect of pHi on the relationship. This suggests that ATP4- is the inhibitory ion species and that the effects of reducing pHi are due to the lowered concentration of ATP4-. 7. Changes in external pH had little effect on either single-channel or whole-cell K+ATP currents. 8. The effects of pHi do not support a role for H+ in linking glucose metabolism to K+ATP channel inhibition in pancreatic beta-cells.

Transport of gentamicin and fluid-phase endocytosis markers in the LLC-PK1 kidney epithelial cell line

In order to characterize the transport of aminoglycoside in the cultured kidney epithelial cell line LLC-PK1, cellular uptake of gentamicin was studied in comparison with those of fluid-phase endocytosis markers, lucifer yellow and horseradish peroxidase. The uptake of gentamicin and fluid-phase markers were time-dependent and were reduced at low temperature. The rate of gentamicin uptake was, however, faster than those of lucifer yellow and horseradish peroxidase, and was saturable. The accumulation of gentamicin in the cells was increasing even after 6 days of incubation, whereas that of lucifer yellow reached a steady state by 1 day. Release of intracellular gentamicin from LLC-PK1 cells was much slower than that of lucifer yellow. Gentamicin uptake, but not lucifer yellow uptake, was increased by reducing the ambient ionic strength. Under the low ionic strength conditions, gentamicin uptake was inhibited by the presence of other aminoglycosides, lysozyme, polyamines such as spermine and inorganic cations such as calcium. These results indicate that gentamicin electrostatically binds to the cell apical membrane and is subsequently taken up by an adsorptive endocytosis in LLC-PK1 cells.

Diabetes-induced reduction of neuronal survival in hypotonic environments in culture

Dorsal root ganglion (DRG) neurons from streptozotocin (STZ)-induced diabetic and normal C57BL mice were exposed to three different hypotonic environments (1/2, 1/4, and 1/8 osmolar solutions). After rapid applications of these hypotonic solutions to the neurons, the cell volume autoregulatory mechanism operated in 1/2 osmolar solution but was disrupted in superhypotonic solutions below 1/4 osmolar in both kinds of mice. None of the neurons could survive 12 h after treatment with superhypotonic solutions. On the other hand, a gradual reduction of osmolarity of the culture medium enabled neurons in the normal mice to survive in 1/2 and 1/4 osmolar solutions as well as in an isotonic solution. However, this reduction of osmolarity increased neuronal cell death in the diabetic mice. These results suggest that the ability of DRG neurons to survive in hypotonic environments in culture may be lost in diabetes.

Fractional mean transit time in transplanted kidneys studied by technetium-99m-DTPA: comparison of clinical and biopsy findings

To determine the usefulness of fractional mean transit time (MTT) in the differential diagnosis of postrenal transplant complications, 99mTc-DTPA was used to evaluate differences in MTT between the outer zone (cortical nephron) and middle zone (juxtamedullary nephron, calcyces and cortical nephron) of the kidney. It is well known that acute rejection is characterized by delayed cortical transit time, whereas cortical nephron function is well maintained and juxtamedullary function is impaired after renal ischemia.

METHODS

Technetium-99m-DTPA fractional MTT was determined by deconvolution analysis of 89 renograms obtained within 5 days of the date of kidney graft biopsy and evaluation.

RESULTS

Outer zone MTT was significantly shorter than middle zone MTT in normals (2.7 +/- 0.4 versus 3.0 +/- 0.6 min, n = 22, p < 0.001), acute tubular necrosis (3.4 +/- 1.1 versus 3.6 +/- 1.4 min, n = 19, p < 0.01), chronic rejection (3.9 +/- 1.5 versus 5.0 +/- 2.3 min, n = 14, p < 0.001) and obstruction (4.1 +/- 0.6 versus 8.9 +/- 3.4 min, n = 13, p < 0.001). In contrast, outer zone MTT was significantly longer than middle zone MTT in acute rejection (4.8 +/- 3.2 versus 4.2 +/- 2.5 min, n = 21, p < 0.05).

CONCLUSION

Fractional MTT was demonstrated to be useful in differentiating acute rejection and ATN in transplanted kidneys.

Wound-induced expression of horseradish peroxidase

Peroxidases have been implicated in the responses of plants to physiological stress and to pathogens. Wound-induced peroxidase of horseradish (Armoracia rusticana) was studied. Total peroxidase activity was increased by wounding in cell wall fractions extracted from roots, stems and leaves of horseradish. On the other hand, wounding decreased the peroxidase activity in the soluble fraction from roots. The enzyme activities of the basic isozymes were induced by wounding in horseradish leaves based on data obtained by fractionation of crude enzyme in isoelectric focusing gel electrophoresis followed by activity staining. We have previously isolated genomic clones for four peroxidase genes, namely, prxC1a, prxC1b, prxC2 and prxC3. Northern blot analysis using gene-specific probes showed that mRNA of prxC2, which encodes a basic isozyme, accumulated by wounding, while the mRNAs for other peroxidase genes were not induced. Tobacco (Nicotiana tabacum) plants were transformed with four chimeric gene constructs, each consisting of a promoter from one of the peroxidase genes and the β-glucuronidase (GUS) structural gene. High level GUS activity induced in response to wounding was observed in tobacco plants containing the prxC2-GUS construct.

Regulatory sequences involved in the peroxidase gene expression in Arabidopsis thaliana

Organ-specific expression of two peroxidase genes (prxCa and prxEa) from Arabidopsis thaliana was studied. The prxCa gene showed non-specific expression with relatively high levels of mRNA accumulation in the roots, stems and leaves of A. thaliana. The prxEa gene, on the other hand, accumulated high levels of mRNA only in roots. Promoter fragments from each gene were fused to the coding region of β-glucuronidase (gusA) reporter gene introduced into tobacco. Promoter/gusA contructs were transferred to tobacco (Nicotiana tabacum BY-2) protoplasts by electroporation or to N. tabacum SR-1 by Agrobacterium tumefaciens-mediated leaf disk transformation. Transient expression in tobacco protoplasts showed that the 580 fragment from prxEa (Ea-580) expressed thirteen-fold and eight-fold higher GUS activity than prxCa (Ca-622) fragment and CaMV35S promoter, respectively. Tobacco plants transformed with the gusA gene, fused to the -580 deletion (Ea-580), exhibited high GUS expression in roots. The root-specific expression of GUS gene was also observed when the -281 bp deletion end point was used. Although the GUS activity in transgenic tobacco under the control of Ca-622 was low, the activity was found in all organs examined. Histochemical analyses of stem and root tissues of Ea-580 showed that the GUS gene was expressed specifically in phloem and pith parenchyma cells. For Ca-622, high level, specific expression of the gusA gene was observed in the xylem of roots. The results of this study implicate multiple cis-elements in the control of transcription from the prxEa promoter.