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H Daniel

Publications and source records attributed to H Daniel.

At least 91 records · Page 5Linked to original sources
PubMed1994

Transport of cefadroxil in rat kidney brush-border membranes is mediated by two electrogenic H+-coupled systems.

The transport characteristics of the aminocephalosporin [3H]cefadroxil have been studied in brush-border membrane vesicles (BBMV) of rat kidney cortex by a rapid filtration technique and by use of a potential sensitive fluorescent dye. Influx of [3H]cefadroxil (0.25 microM) into BBMV as a function of time displayed a pronounced overshoot phenomenon in the presence of a transmembrane pH gradient (pHin > pHout). Evidence for an electrogenic cefadroxil/H+-symport in the presence of an inwardly directed proton gradient is provided by the demonstration of: 1) reduced uptake in the presence of a protonophore; 2) reduced uptake under voltage clamp conditions; and 3) increased uptake in the presence of a valinomycin-induced inside negative K+-diffusion potential. pH-gradient dependent uptake of [3H]cefadroxil as a function of substrate concentration revealed the presence of multiple carrier systems. By kinetic analysis, a high-affinity carrier system (Km, 8.8 +/- 1.3 microM) and a low-affinity system (Km, 2.62 +/- 0.80 mM) could be resolved. The high-affinity transport system was found to be very specific for substrates (cephalosporins and di- and tripeptides) carrying an alpha-amino group. By use of a potential sensitive fluorescent dye 3,3'-dipropylthiadicarbocyanine iodide, the low-affinity transport system was characterized with respect to its driving force and its kinetic features. This transporter was found also to be electrogenic in nature, representing a second cefadroxil/H+-symport system. In summary, our studies demonstrate for the first time uphill transport of cefadroxil in kidney BBMV mediated by multiple carrier systems. Transport is rheogenic, energized by the proton motive force and shared by other aminocephalosporins as well as di- and tripeptides.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Long-term depression requires nitric oxide and guanosine 3':5' cyclic monophosphate production in rat cerebellar Purkinje cells.

In patch-clamped Purkinje cells, bath application of the nitric oxide synthase inhibitor NG-methyl-L-arginine consistently prevents the induction of long-term depression (LTD) of parallel fibre-mediated excitatory postsynaptic potentials (EPSPs) induced by their pairing with calcium spikes. On the other hand, bath application of nitric oxide donors and of 8-bromoguanosine 3':5' cyclic monophosphate is able to reproduce an LTD-like phenomenon. LTD of parallel fibre-mediated EPSPs also occurs when nitric oxide donors or guanosine 3':5' cyclic monophosphate are directly dialysed into Purkinje cells, and this effect partially occludes LTD induced by pairing protocols. These results show that nitric oxide does play a role in LTD induction, and demonstrate for the first time that its site of action is probably the soluble guanylate cyclase of Purkinje cells.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1993

Removal of glycylglutamine from plasma by individual tissues: mechanism and impact on amino acid fluxes in postabsorption and starvation.

A possible source of glutamine, for inclusion in the parenteral solutions, is glycylglutamine. The aim of this article is to review briefly the information on metabolism of glycylglutamine when administered intravenously. The fact that there is efficient utilization of intravenously infused glycylglutamine was evident with very little excretion in the urine. Although all the tissues examined, except brain, participated in the removal of glycylglutamine from plasma, kidney predominated in this regard. This may be related to the presence of carrier-mediated systems for cellular uptake of glycylglutamine in the kidney and the lack of them in other tissues. Starvation did not alter the metabolic clearance of glycylglutamine, although it reduced the removal by the kidney. Renal metabolism of glycylglutamine resulted in the release of constituent amino acids that were largely utilized by the liver in the postabsorptive state and by skeletal muscle in starvation. This alteration was accompanied by a selective inhibition of muscle release of amino acids that are substrates for enhanced hepatic gluconeogenesis and renal ammoniagenesis in starvation. Because there was no change either in plasma glucose level or ammonia excretion during the infusion of glycylglutamine in starved human subjects, apparently the amino acid residues of glycylglutamine fulfilled the substrate needs for these functions. These results provide a metabolic basis for further investigations of the possible nutritional benefit of including glycylglutamine in parenteral nutrition.

Amino Acids↗
PubMed1993

Effects of phosphorylation of chrysotile on pleuropulmonary fibrogenicity and carcinogenicity.

As well as fibre size, fibre chemistry is a determinant of toxicity of mineral fibres. On these grounds, a few years ago, the asbestos industry in Québec developed a process to modify the surface chemistry of chrysotile asbestos by fixing phosphorous atoms. The pleuropulmonary fibrogenicity and carcinogenicity of the native and surface treated chrysotile, called chrysophosphate, were tested. Both products initiated similar pulmonary fibrogenicity in rats exposed by inhalation and sheep exposed by injection in the tracheal lobe. Tumour production in rats after long term inhalation or intrapleural injection was not different between chrysotile and chrysophosphate. These findings clearly show that modification of the phosphate surface of chrysotile fibres does not appear to alter the pleuropulmonary activities of the mineral, thus arguing against the earlier contention of less biological activity for chrysophosphate, a contention essentially based upon results of in vitro tests. This study strongly argues for in vivo testing of new fibrous materials before making definite conclusions about their biological activities.

Animals↗
PubMed1993

Transport of beta-lactam antibiotics in kidney brush border membrane. Determinants of their affinity for the oligopeptide/H+ symporter.

This study was designed to determine whether beta-lactam antibiotics (cephalosporins and penicillins) are all substrates for the renal oligopeptide/H+ symporter and, if so, whether the transport system discriminates among the numerous beta-lactam antibiotics. We used [3H]glycylglutamine, [3H]cephalexin, and [3H]-ampicillin as probes for the transport of oligopeptides, cephalosporins, and penicillins in kidney brush border membrane vesicles, respectively. Among the beta-lactam antibiotics, only those with an alpha-amino group in the phenylacetamido moiety were found to interact with the oligopeptide/H+ symporter. Aminocephalosporins displayed high affinities (KiS generally < 250 microM), whereas aminopenicillins displayed low affinities (Ki 0.78-3.03 mM). These differences in affinities appeared to be a consequence of conformational features of the substrates, especially the sterical location of the carboxy group. The affinities of aminolactams for the oligopeptide/H+ symporter were, furthermore, related to the hydrophobicity of the phenylglycyl chains and the substituents attached to the thiazolidine and dihydrothiazine ring. In sharp contrast to the uptake of [3H]glycylglutamine and [3H]cephalexin, the uptake of [3H]ampicillin was not dependent on a pH gradient and was inhibited by various beta-lactam antibiotics, whether or not they contained an alpha-amino group. Our data suggest that: (a) the transport of aminocephalosporins is largely mediated by the oligopeptide/H+ symporter, which is highly influenced by the substrate structure; and (b) penicillins are transported by another system, which is less discriminative with respect to substrate structure.

Ampicillin↗
PubMed1993

Dipeptides in parenteral nutrition: from basic science to clinical applications.

The use of intravenous dipeptides shows great promise as an avenue for the provision of amino acids that may otherwise be difficult to deliver via nutrient infusions. The physical/chemical properties and metabolism of numerous dipeptides have now been explored in experimental and human studies. It has been found that these agents have the capacity to spare nitrogen and support serum protein levels in a fashion equivalent to that of intravenous free amino acids. An additional benefit is the ability to deliver certain amino acids that are relatively unstable or poorly soluble in aqueous solutions. These various aspects of intravenous dipeptides are considered in this review.

Animals↗
PubMed1992

Determinants of substrate affinity for the oligopeptide/H+ symporter in the renal brush border membrane.

We and others have shown previously the existence of high and low affinity systems for oligopeptide transport in kidney brush border membrane vesicles (BBMV). In the present study we investigated the relationship between the structure of substrates and their affinity for interaction with the high-affinity oligopeptide/H+ transporter in kidney BBMV. Based on competition experiments using [3H]Gly-Gln as a probe we determined the Ki values for more than 60 selected peptides. For a high-affinity interaction with the carrier site the following structural features of substrates are required: (a) both a free amino and carboxyl terminus; (b) the amino group and peptide bond nitrogen located in the alpha-position; (c) a trans peptide bond rather than the cis configuration; (d) L-alpha-amino acid isomers in both COOH and NH2 termini, although D-isomers of hydrophobic amino acids are acceptable in the NH2 terminus; and (e) a backbone of less than 3 amino acid residues. A striking finding of the present study is that, for peptides satisfying these minimal structural requirements, the primary determinant of affinity is hydrophobicity. The fact that there is a highly significant (p less than 0.001) correlation between Ki and hydrophobicity allows the prediction of the affinity for any di- or tripeptide composed of alpha-amino acids in the L-form.

Amino Acid Sequence↗
PubMed1992

Cerebellar nuclei and the nucleocortical projections in the rat: retrograde tracing coupled to GABA and glutamate immunohistochemistry.

The amino acids GABA and glutamate (Glu) are thought to be the principal substances in the central nervous system responsible for neuronal inhibition and excitation. Their distributions among the different neurons in a defined pathway may thus be indicative of the contributions of the cells to pathway function. Examples of such neurons are those of the cerebellar nuclei which, while regulating output from the Purkinje cells of the cerebellar cortex, are also found to project back to the cerebellar cortex. Immunohistochemical experiments were done to identify GABA and glutamate (Glu) containing cells in the adult rat cerebellar nuclei. Consecutive semithin and serial vibratome sections were incubated with antisera raised in rabbit against GABA and Glu. In semithin sections, only small neurons were intensely GABA immunoreactive (GABA-IR) (31.7%), and the majority (80.5%) were Glu immunoreactive (Glu-IR) of different sizes. Consistent with Glu being a metabolic precursor for GABA, 75.4% of the GABA-IR population colocalized Glu. In vibratome sections GABA-IR neurons showed some local differences in number, whereas the Glu-IR were uniformly distributed in the three nuclei studied. Measured mean diameters for these neurons showed a distinct size difference for the GABA- and Glu-IR with little overlap. Cerebellar nuclei neurons projecting to the cortex (nucleocortical neurons, NCN) were identified by locally preinjecting the retrograde transported WGA-apoHRP-colloidal gold complex in the cerebellar cortex. Vibratome sections of these cerebellar were silver intensified for the retrograde tracer and double labeled for GABA and Glu. Of the total number of identified NCN, 8.7% were GABA-IR (10 animals) and 47.7% Glu-IR (5 animals). Many retrograde labeled NCN in the core of the thick sections were immunonegative for both amino acids due to poor antibody penetration, thus underestimating the proportions of cells containing GABA and Glu. The size distributions for the GABA-IR and Glu-IR NCN were similar to those measured in non-retrograde labeled nuclei in thick sections. The conclusions reached are that GABA-IR neurons of the cerebellar nuclei, including the NCN, use GABA as the presumed inhibitory neurotransmitter and that Glu-IR neurons may use Glu or another excitatory neurotransmitter.

Afferent Pathways↗
PubMed1992

Coactivation of metabotropic glutamate receptors and of voltage-gated calcium channels induces long-term depression in cerebellar Purkinje cells in vitro.

Using an in vitro slice preparation, we studied the effects, on parallel fiber (PF)-mediated EPSPs, of coactivation of metabotropic-glutamate receptors and of voltage-gated calcium (Ca) channels of Purkinje cells (PCs) by bath application of 50 microM trans-1-amino-cyclopentyl-1,3-dicarboxylate (trans-ACPD) and by direct depolarization of the cells, respectively. These effects were compared with changes in synaptic efficacy obtained when alpha-amino-3hydroxy-5-methylisoxalone-4-propionate (AMPA) receptors of PCs were also activated through stimulation of PFs during the pairing protocol, as well as when similar experiments were performed without trans-ACPD in the bath. In a control medium, pairing for 1 min of PF-mediated EPSPs evoked at 1 Hz with Ca spikes evoked by steady depolarization of PCs (n = 13) led to LTD of synaptic transmission in 9 cases whereas for the others EPSPs were not affected. No LTD occurred in 9 out of 10 other cells tested when PF stimulation was omitted during the 1 min period of Ca spike firing of PCs. Bath application of 50 microM trans-ACPD, in conjunction with the same pairing protocol as before (n = 8), led to a significantly larger LTD of PF-mediated EPSPs after washing out of this drug. Moreover, a clear-cut LTD of PF-mediated EPSPs was also observed in 5 of the 8 other cells, when PF stimulation was omitted during Ca spike firing in the presence of trans-ACPD.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Sodium-dependent transport of riboflavin in brush border membrane vesicles of rat small intestine is an electrogenic process.

Transport of riboflavin across the intestinal brush border membrane in rats was studied using the brush border membrane vesicle technique. Uptake of riboflavin into the membrane vesicles was predominantly the result of transport into an osmotically reactive space. Binding of the substrate to the membrane surface increased as a function of time and with lowering of the incubation buffer pH. The transport of riboflavin at low substrate concentrations was carrier mediated and Na+, but not K+, dependent with a distinct overshoot phenomenon. Uptake as a function of substrate concentration revealed dual transport characteristics in the presence of a Na+ gradient but linearity in the presence of a K+ gradient. The apparent Km value of the saturable, carrier-mediated and Na(+)-dependent component was calculated by two independent methods to be 0.25 or 0.38 mumol/L. Because uptake of riboflavin into brush border membrane vesicles in the presence of a Na+ gradient was increased by a valinomycin-induced K(+)-diffusion potential and by sodium thiocyanate vs. NaCl (intravesicular negative membrane potential), riboflavin transport is most likely an electrogenic process. The Na(+)-dependent riboflavin uptake into the vesicles was inhibited by structural analogues at low substrate concentrations only and increased by a low buffer pH.

Animals↗
PubMed1992

Oligopeptides: mechanism of renal clearance depends on molecular structure.

We have investigated the relative contribution of hydrolysis, intact transport and urinary excretion to the renal clearance of Gly-Sar, Gly-Sar-Sar, and Gly-Gly-Sar in fed and starved rats. The results obtained from isolated kidney perfusion studies are summarized as follows: 1) clearance was fastest for Gly-Gly-Sar and slowest for Gly-Sar-Sar, 2) urinary excretion of Gly-Sar-Sar exceeded that of Gly-Gly-Sar or Gly-Sar, 3) there was accumulation of products of hydrolysis of Gly-Gly-Sar in the perfusate but not of Gly-Sar or Gly-Sar-Sar, 4) isolated brush-border and basolateral membranes of renal tubular cells lacked hydrolytic activity against Gly-Sar and Gly-Sar-Sar but possessed hydrolytic activity against Gly-Gly-Sar, 5) an excess amount of Gly-Sar-Sar reduced the rate of clearance of Gly-Gly-Sar by approximately 40% and significantly increased urinary excretion of this peptide, 6) the nonfiltering kidney cleared Gly-Gly-Sar at a rate which was 50% of that of the filtering kidney but did not clear Gly-Sar, and 7) starvation for 96 h was without a significant effect on the renal clearance of either Gly-Sar or Gly-Sar-Sar but significantly reduced the renal clearance of Gly-Gly-Sar and the brush-border membrane hydrolase activity against this peptide. We conclude that the molecular structure determines the affinity of oligopeptides for the membrane transport and hydrolytic systems, which, in turn, determines their efficiency for clearance by the kidney.

Animals↗
PubMed1991

Sensitivity of rubrospinal neurons to excitatory amino acids in the rat red nucleus in vivo.

Responses of rubrospinal neurons (RSNs) to iontophoretic applications of L-glutamate (L-Glu), L-aspartate (L-Asp), quisqualate (Quis) and N-methyl-D-aspartate (NMDA) have been studied in the rat red nucleus (RN) in vivo. All agonists produced a dose-dependent increase of the firing rate and Quis was found to be the most efficient. The responses to NMDA and to a lesser extent to L-Asp were abolished by steady application of 2-amino-5-phosphonovalerate (2APV) whereas responses to Quis were unaffected and those to L-Glu poorly antagonized. On the other hand, NMDA-mediated excitations were insensitive to steady application of 6,7-dinitroquinoxaline-2,3-dione (DNQX) which abolished responses to Quis and to a lesser extent to L-Glu while those to L-Asp were less affected. These results show the presence of both NMDA and non-NMDA receptors on RSNs in the rat. A specific localization of the NMDA receptors on distal dendrites of these neurons is suggested.

2-Amino-5-phosphonovalerate↗
PubMed1991

The high and low affinity transport systems for dipeptides in kidney brush border membrane respond differently to alterations in pH gradient and membrane potential.

The principal aim of the present study was to investigate the effects of variation in proton gradient and membrane potential on the transport of glycyl-L-glutamine (Gly-Gln) by renal brush border membrane vesicles. Under our conditions of transport assay, Gly-Gln was taken up by brush border membrane vesicles almost entirely as intact dipeptide. This uptake was mediated by two transporters shared by other dipeptides and characterized as the high affinity (Kt = 44.1 +/- 11.2 microM)/low capacity (Vmax = 0.41 +/- 0.03 nmol/mg protein/5 s) and low affinity (Kt = 2.62 +/- 0.50 mM)/high capacity (Vmax 4.04 +/- 0.80 nmol/mg protein/5 s) transporters. In the absence of a pH gradient, only the low affinity system was operational, but with a reduced transport capacity. Imposing a pH gradient of 1.6 pH units increased the Vmax of both transporters. Kinetic analysis of the rates of Gly-Gln uptake as a function of external pH revealed Hill coefficients of close or equal to 1, indicating that transporters contain only one binding site for the interaction with external H+. The effects of membrane potential on Gly-Gln uptake were investigated with valinomycin-induced K+ diffusion potentials. The velocity of the high affinity system but not of the low affinity system increased linearly with increasing inside-negative K+ diffusion potentials (p less than 0.01). The Kt of neither system was affected by alterations in either pH gradient or membrane potential. We conclude that (a) the high affinity transporter is far more sensitive to changes in proton gradient and membrane potential than the low affinity transporter and (b) in the presence of a pH gradient, transport of each dipeptide molecule requires cotransport of one hydrogen ion to serve as the driving force.

Animals↗