Nucleotide inhibition of phosphate transport in the renal proximal tubule

1983 ◽  
Vol 245 (2) ◽  
pp. F263-F271
Author(s):  
R. P. Lang ◽  
N. Yanagawa ◽  
E. P. Nord ◽  
L. Sakhrani ◽  
S. H. Lee ◽  
...  
Keyword(s):  
Proximal Tubule ◽  
Competitive Inhibition ◽  
Specific Activity ◽  
Direct Action ◽  
Dilution Effect ◽  
Phosphate Transport ◽  
Inhibitory Effect ◽  
P Uptake ◽  
Luminal Membrane ◽  
P Flux

The observation that NAD inhibits sodium-dependent phosphate (P) uptake by the luminal brush border membrane (BBM) of the proximal tubule prompted us to examine the specificity and mechanism of this process. Addition of 10(-5) M NAD to the perfusate of isolated perfused rabbit proximal straight tubules inhibited lumen-to-bath P flux by approximately 50%. ADP-ribose had an identical effect, whereas nicotinamide had no effect. ADP and 5'-AMP (10(-5) M) also inhibited P flux. Na-dependent uptake of 32P by rabbit BBM vesicles was inhibited by 0.1-0.3 mM NAD, ADP-ribose, ADP, ATP, 5'-AMP, and GDP, which were preincubated with the vesicles for 30 min. The kinetics of inhibition showed an apparent increase in the Km for P but no change in Vmax. These findings are consistent with "competitive inhibition." The nucleotides inhibited P uptake even when BBM alkaline phosphatase was inhibited by 96% with 10 mM theophylline. Evidence of nonspecific phosphatase activity was present, since incubation of BBM with 0.1 mM solution of nucleotides for 30 min resulted in an elevation of free P in the medium of approximately 0.15-0.22 mM. Correction of 32P specific activity for this change resulted in values for Km and Vmax that were not significantly different from control. The "competitive inhibition" could thus be ascribed to an isotope-dilution effect. There was no evidence to suggest that NAD caused ADP-ribosylation of the luminal membrane. These studies indicate that adenine and guanine nucleotides do not inhibit P transport by a direct action on the luminal membrane of the proximal tubule but do inhibit lumen-to-bath P flux in isolated perfused proximal tubules at concentrations of 10(-5) M. Since there is no direct inhibitory effect of these compounds at the level of the BBM, it is possible that they inhibit P transport by altering some event subsequent to the transfer of P across the luminal membrane.

scholarly journals Signaling pathways utilized by PTH and dopamine to inhibit phosphate transport in mouse renal proximal tubule cells

2009 ◽  
Vol 296 (2) ◽  
pp. F355-F361 ◽  
Author(s):  
Rochelle Cunningham ◽  
Rajatsubhra Biswas ◽  
Marc Brazie ◽  
Deborah Steplock ◽  
Shirish Shenolikar ◽  
...  
Keyword(s):  
Proximal Tubule ◽  
Signaling Pathways ◽  
Phosphate Transport ◽  
Inhibitory Effect ◽  
Renal Proximal Tubule ◽  
Proximal Tubule Cells ◽  
Phosphate Cotransport ◽  
Tubule Cells ◽  
Renal Proximal Tubule Cells ◽  
Sodium Phosphate Cotransport

The present experiments were designed to detail factors regulating phosphate transport in cultured mouse proximal tubule cells by determining the response to parathyroid hormone (PTH), dopamine, and second messenger agonists and inhibitors. Both PTH and dopamine inhibited phosphate transport by over 30%. The inhibitory effect of PTH was completely abolished in the presence of chelerythrine, a PKC inhibitor, but not by Rp-cAMP, a PKA inhibitor. By contrast, both chelerythrine and Rp-cAMP blocked the inhibitory effect of dopamine. Chelerythrine inhibited PTH-mediated cAMP accumulation but also blocked the inhibitory effect of 8-bromo-cAMP on phosphate transport. On the other hand, Rp-cAMP had no effect on the ability of DOG, a PKC activator, to inhibit phosphate transport. PD98059, an inhibitor of MAPK, had no effect on PTH- or dopamine-mediated inhibition of sodium-phosphate cotransport. Finally, compared with 8-bromo-cAMP, 8-pCPT-2′- O-Me-cAMP, an activator of EPAC, had no effect on phosphate transport. These results outline significant differences in the signaling pathways utilized by PTH and dopamine to inhibit renal phosphate transport. Our results also suggest that activation of MAPK is not critically involved in PTH- or dopamine-mediated inhibition of phosphate transport in mouse renal proximal tubule cells in culture.

Effect of norepinephrine on intracellular pH in kidney proximal tubule: role of Na+-( HCO 3 − ) n cotransport

1998 ◽  
Vol 275 (1) ◽  
pp. F33-F45 ◽  
Author(s):  
Solange Abdulnour-Nakhoul ◽  
Raja N. Khuri ◽  
Nazih L. Nakhoul
Keyword(s):  
Membrane Potential ◽  
Proximal Tubule ◽  
Intracellular Ph ◽  
Basolateral Membrane ◽  
Inhibitory Effect ◽  
Rate Of Change ◽  
Kidney Proximal Tubule ◽  
Luminal Membrane ◽  
Basolateral Membrane Potential

We examined the effect of norepinephrine (NE) on intracellular pH (pHi) and activity of Na+([Formula: see text]) in the isolated perfused kidney proximal tubule of Ambystoma, using single-barreled voltage and ion-selective microelectrodes. In control[Formula: see text] Ringer, addition of 10−6 M NE to the bath reversibly depolarized the basolateral membrane potential ( V 1), the luminal membrane potential ( V 2), and the transepithelial potential difference ( V 3) and increased pHi by 0.14 ± 0.02. These effects were mimicked by isoproterenol but were abolished after pretreatment with SITS or in the absence of CO2/[Formula: see text]. Removal of bath Na+ depolarized V 1 and V 2, hyperpolarized V 3, and decreased pHi. These effects are largely mediated by the electrogenic Na+-([Formula: see text]) n cotransporter. In the presence of NE, the effects of Na+ removal on membrane potential differences and the rate of change of pHi were significantly smaller. Reducing bath [Formula: see text] concentration from 10 to 2 mM at constant CO2 (pH 6.8) depolarized V 1 and V 2, decreased pHi, and lowered[Formula: see text]. These changes are also due to Na+-([Formula: see text]) n . In the presence of NE, reducing bath [[Formula: see text]] caused a smaller depolarizations of V 1 and V 2, and the rate of pHi decrease was significantly reduced. Our results indicate: 1) NE causes an increase in pHi; 2) the NE-induced alkalinization is mediated by a SITS-sensitive and[Formula: see text]-dependent transporter on the basolateral membrane; and 3) in the presence of NE, the reduced effects caused by basolateral[Formula: see text] changes or Na+ removal are indicative of an inhibitory effect of NE on Na+-([Formula: see text]) n cotransport.

MODE OF ACTION OF CLOMIPHENE

1969 ◽  
Vol 60 (4) ◽  
pp. 635-644 ◽  
Author(s):  
J. Hammerstein
Keyword(s):  
Mode Of Action ◽  
Specific Activity ◽  
Direct Action ◽  
Clomiphene Citrate ◽  
Inhibitory Effect ◽  
Isotopic Dilution ◽  
Corpora Lutea ◽  
Isolation And Purification

ABSTRACT The in vitro influence of clomiphene citrate on the incorporation of acetate-1-14C into progesterone by slices of human corpora lutea was studied in 10 experiments using the reverse isotopic dilution technique for the isolation and purification of radioactive progesterone, followed in most instances by crystallization to constant specific activity. As a clear-cut and reproducible result, the formation of progesterone from labelled acetate was considerably diminished in the presence of clomiphene citrate independent of whether the tissues originated from the menstrual cycle or from normal as well as ectopic pregnancies. This inhibitory effect on the biosynthesis of progesterone was intensified by increasing the concentration of clomiphene in the medium. It was demonstrable after 13.3 minutes of incubation as well as after 6 hours. No obvious interference of clomiphene with the stimulating action of HCG on steroidogenesis was found. These findings point to a direct action of clomiphene on the ovary which might also have some bearing on the mode of action of clomiphene in vivo.

Tubular transport responses to angiotensin

1985 ◽  
Vol 248 (5) ◽  
pp. F621-F630 ◽  
Author(s):  
P. J. Harris ◽  
L. G. Navar
Keyword(s):  
Proximal Tubule ◽  
Sodium Excretion ◽  
Direct Action ◽  
Extracellular Volume ◽  
Ang Ii ◽  
Cellular Mechanisms ◽  
Renal Vasculature ◽  
Luminal Membrane ◽  
Proximal Tubular ◽  
High Doses

Angiotensin II (ANG II) is a powerful effector agent in the regulation of extracellular volume and exerts an important influence on renal sodium excretion. In addition to its effects on aldosterone secretion, ANG II acts directly on the kidney causing retention of sodium at low (physiological) doses and enhanced sodium excretion at high doses. The mechanism for these responses involves vasoconstrictor actions of ANG II on the renal vasculature and a direct action of the peptide on tubular reabsorption. Micropuncture and microperfusion studies have demonstrated that proximal tubular sodium and water transport are stimulated by physiological concentrations (10(-12) to 10(-10) M) of ANG II on the peritubular side, whereas higher doses (10(-7) M) cause inhibition. A luminal site of action in the proximal tubule has also been reported and additional more distal sites are indicated. [125I]ANG II binding sites on the brush border and basolateral membranes of proximal tubule cells have high affinity (Kd in the nanomolar range) for ANG II and lower affinity for ANG III. The biphasic action of ANG II is exerted directly on the epithelial cells and appears to be electroneutral. The data indicate that ANG II binds to receptors on the basolateral cell membrane and alters the rate of entry of sodium through the luminal membrane to increase or decrease, depending on the concentration of peptide. Several possible cellular mechanisms that could mediate these responses are discussed.

Effects of Dipyrone on Prostaglandin Production by Human Platelets and Cultured Bovine Aortic Endothelial Cells

1983 ◽  
Vol 49 (02) ◽  
pp. 132-137 ◽  
Author(s):  
A Eldor ◽  
G Polliack ◽  
I Vlodavsky ◽  
M Levy
Keyword(s):  
Endothelial Cells ◽  
Arachidonic Acid ◽  
Competitive Inhibition ◽  
Inhibitory Effect ◽  
Human Platelets ◽  
Ionophore A23187 ◽  
Aortic Endothelial Cells ◽  
Bovine Aortic Endothelial Cells ◽  
Aortic Endothelial

SummaryDipyrone and its metabolites 4-methylaminoantipyrine, 4-aminoantipyrine, 4-acetylaminoantipyrine and 4-formylaminoan- tipyrine inhibited the formation of thromboxane A2 (TXA2) during in vitro platelet aggregation induced by ADP, epinephrine, collagen, ionophore A23187 and arachidonic acid. Inhibition occurred after a short incubation (30–40 sec) and depended on the concentration of the drug or its metabolites and the aggregating agents. The minimal inhibitory concentration of dipyrone needed to completely block aggregation varied between individual donors, and related directly to the inherent capacity of their platelets to synthesize TXA2.Incubation of dipyrone with cultured bovine aortic endothelial cells resulted in a time and dose dependent inhibition of the release of prostacyclin (PGI2) into the culture medium. However, inhibition was abolished when the drug was removed from the culture, or when the cells were stimulated to produce PGI2 with either arachidonic acid or ionophore A23187.These results indicate that dipyrone exerts its inhibitory effect on prostaglandins synthesis by platelets or endothelial cells through a competitive inhibition of the cyclooxygenase system.

Inhibition of Yeast Growth by Tryptamine and Recovery with Tryptophan

2020 ◽  
Vol 16 (1) ◽  
pp. 48-52 ◽  
Author(s):  
Chandrika Kadkol ◽  
Ian Macreadie
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Carbon Source ◽  
Competitive Inhibition ◽  
Yeast Species ◽  
Inhibitory Effect ◽  
The Body ◽  
Inhibitory Effects ◽  
Trna Synthetases ◽  
Fermentative Growth ◽  
Biogenic Monoamine

Background: Tryptamine, a biogenic monoamine that is present in trace levels in the mammalian central nervous system, has probable roles as a neurotransmitter and/or a neuromodulator and may be associated with various neuropsychiatric disorders. One of the ways tryptamine may affect the body is by the competitive inhibition of the attachment of tryptophan to tryptophanyl tRNA synthetases. Methods: This study has explored the effects of tryptamine on growth of six yeast species (Saccharomyces cerevisiae, Candida glabrata, C. krusei, C. dubliniensis, C. tropicalis and C. lusitaniae) in media with glucose or ethanol as the carbon source, as well as recovery of growth inhibition by the addition of tryptophan. Results: Tryptamine was found to have an inhibitory effect on respiratory growth of all yeast species when grown with ethanol as the carbon source. Tryptamine also inhibited fermentative growth of Saccharomyces cerevisiae, C. krusei and C. tropicalis with glucose as the carbon source. In most cases the inhibitory effects were reduced by added tryptophan. Conclusion: The results obtained in this study are consistent with tryptamine competing with tryptophan to bind mitochondrial and cytoplasmic tryptophanyl tRNA synthetases in yeast: effects on mitochondrial and cytoplasmic protein synthesis can be studied as a function of growth with glucose or ethanol as a carbon source. Of the yeast species tested, there is variation in the sensitivity to tryptamine and the rescue by tryptophan. The current study suggests appropriate yeast strains and approaches for further studies.

scholarly journals A novel role for WAVE1 in controlling actin network growth rate and architecture

2015 ◽  
Vol 26 (3) ◽  
pp. 495-505 ◽  
Author(s):  
Meredith O. Sweeney ◽  
Agnieszka Collins ◽  
Shae B. Padrick ◽  
Bruce L. Goode
Keyword(s):  
Actin Filament ◽  
Specific Activity ◽  
Inhibitory Effect ◽  
Actin Network ◽  
Inhibitory Effects ◽  
Cellular Functions ◽  
Network Growth ◽  
Assembly Kinetics ◽  
Filament Networks ◽  
First Time

Branched actin filament networks in cells are assembled through the combined activities of Arp2/3 complex and different WASP/WAVE proteins. Here we used TIRF and electron microscopy to directly compare for the first time the assembly kinetics and architectures of actin filament networks produced by Arp2/3 complex and dimerized VCA regions of WAVE1, WAVE2, or N-WASP. WAVE1 produced strikingly different networks from WAVE2 or N-WASP, which comprised unexpectedly short filaments. Further analysis showed that the WAVE1-specific activity stemmed from an inhibitory effect on filament elongation both in the presence and absence of Arp2/3 complex, which was observed even at low stoichiometries of WAVE1 to actin monomers, precluding an effect from monomer sequestration. Using a series of VCA chimeras, we mapped the elongation inhibitory effects of WAVE1 to its WH2 (“V”) domain. Further, mutating a single conserved lysine residue potently disrupted WAVE1's inhibitory effects. Taken together, our results show that WAVE1 has unique activities independent of Arp2/3 complex that can govern both the growth rates and architectures of actin filament networks. Such activities may underlie previously observed differences between the cellular functions of WAVE1 and WAVE2.

ENZYMIC CHANGES IN THE CERVIX OF THE RAT AND HAMSTER DURING THE OESTROUS CYCLE AND THE EFFECT OF STEROIDS

1977 ◽  
Vol 72 (2) ◽  
pp. 153-161 ◽  
Author(s):  
ELIZABETH ZACHARIAH ◽  
N. R. MOUDGAL
Keyword(s):  
Alkaline Phosphatase ◽  
Specific Activity ◽  
Protein Biosynthesis ◽  
Hydrolytic Enzymes ◽  
Maximal Activity ◽  
Inhibitory Effect ◽  
Oestrous Cycle ◽  
Single Subcutaneous Injection ◽  
Arylsulphatase A ◽  
Phosphatase Alkaline

SUMMARY Changes in four hydrolytic enzymes, namely acid phosphatase, alkaline phosphatase, arylsulphatase A and B, of the cervix of the rat and hamster have been studied during the 4-day oestrous cycle. All four enzymes showed maximal activity on the day of oestrus and least activity on day 2 of dioestrus. All the enzymes showed significant reduction of activity after ovariectomy, arylsulphatase A and B showing the earliest changes in specific activity. A single subcutaneous injection of 0·02 μg oestradiol-17β/rat increased the specific activity of arylsulphatase A and B from the low ovariectomized level to that observed in control oestrous animals within 18 and 6 h respectively. A higher concentration of oestradiol-17β (2·0 μg) had an inhibitory effect. Progesterone was without effect on arylsulphatase B activity, but when given (2·0 mg) with 0·02 μg oestradiol-17β, it inhibited the response to oestrogen. Cycloheximide prevented the rise in arylsulphatase B activity occurring after oestrogen injection, suggesting a regulation of cervical arylsulphatase B at the level of protein biosynthesis. These results suggest that arylsulphatase B activity may be induced by oestrogen in the cervix of the rat.

scholarly journals Biochemical characterisation of α-glucosidase and β-glucosidase in the alimentary canal of larval Leptinotarsa decemlineata SAY, 1824 (Coleoptera: Chrysomelidae)

2014 ◽  
Vol 83 (4) ◽  
pp. 281-294 ◽  
Author(s):  
Majid Kazzazi ◽  
Fahimeh Dehghanikhah ◽  
Hossein Madadi ◽  
Vahid Hossseininaveh
Keyword(s):  
Incubation Time ◽  
Leptinotarsa Decemlineata ◽  
Digestive Enzymes ◽  
Specific Activity ◽  
Inhibitory Effect ◽  
Maximum Activity ◽  
Pest Population ◽  
Biochemical Characterisation ◽  
Leptinotarsa Decemlineata Say ◽  
Environmentally Safe

ABSTRACT Host plant resistance is an environmentally safe method used for reducing a pest population. Basically, when developing resistant cultivars one needs to study the biochemical characteristics of the digestive enzymes in the insect’s midgut. In this study, the activities of α- and β-glucosidase were determined from Leptinotarsa decemlineata midgut using p-nitrophenyl-α-Dglucopyranoside and p-nitrophenyl-β-D-glucopyranoside as substrates respectively. The results showed that the specific activity of α- and β-glucosidase from 4th instar larvae midguts of L. decemlineata were 5.14 and 5.48 Umg-1 protein respectively. The activity of α-glucosidase was optimal at pH 4, whereas the maximum activity of β-glucosidase in the midgut of L. decemlineata occurred at pH 4-5.5. Both enzymes were stable at pH 3-8 over an incubation time of 8 hours. The respective activities of α- and β-glucosidase were at their highest at 45 °C and 50 °C, but they were not stable at 50 °C during an incubation time of 8 days. Furthermore, our data showed that MgCl2, Tris and urea have a moderate but SDS a severe inhibitory effect on enzyme activity. Biochemical characterisation revealed one and three bands of α- and β-glucosidase activities in the midgut of L. decemlineata respectively.

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