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J F Koerner

Publications and source records attributed to J F Koerner.

15 recordsLinked to original sources
PubMed1992

Quisqualic acid analogues: synthesis of beta-heterocyclic 2-aminopropanoic acid derivatives and their activity at a novel quisqualate-sensitized site.

Hippocampal CA1 pyramidal cell neurons are sensitized over 30-fold to depolarization by L-2-amino-4-phosphonobutanoic acid (L-AP4) following exposure to L-quisqualic acid. This phenomenon has been termed the QUIS effect. In the present study several novel L-quisqualic acid analogues have been synthesized and tested for their interaction with the different components of the QUIS-effect system. Replacement of the oxadiazolidinedione ring of L-quisqualic acid with several other types of heterocyclic rings yielded the following quisqualic acid analogues: maleimide 2, N-methylmaleimide 3, N-(carboxymethyl)maleimide 4, succinimides 5A and 5B, and imidazolidinedione 6. None of these analogues were able to mimic the effects of L-quisqualic acid and sensitize hippocampal CA1 neurons to depolarization by L-AP4. Also, unlike L-serine O-sulfate, L-homocysteinesulfinic acid, or L-alpha-aminoadipic acid, none of the analogues were able to preblock or reverse the QUIS effect. However, when the IC50 values for inhibition of the CA1 synaptic field potential of analogues 2-6 were determined both before and after hippocampal slices were exposed to L-quisqualic acid, the IC50 values of analogues 3 and 4 were found to decrease more than 7-fold. Thus, these two compounds behave like L-AP4 rather than L-quisqualic acid in this system in that they exhibit increased potencies in slices that have been pretreated with L-quisqualic acid even though they cannot themselves induce this sensitization. Compounds 3 and 4, therefore, represent the first non-phosphorus-containing compounds to which hippocampal neurons become sensitized following exposure to L-quisqualic acid. No change in the IC50 values was observed for 5A or 5B. Analogues 2 and 6, on the other hand, displayed a high potency for inhibition of the evoked field potential even prior to treatment of the slices with L-quisqualic acid.

Aminobutyrates↗
PubMed1992

Structure-function relationships for analogues of L-2-amino-4-phosphonobutanoic acid on the quisqualic acid-sensitive AP4 receptor of the rat hippocampus.

Hippocampal CA1 pyramidal cell neurons are sensitized to depolarization by L-2-amino-4-phosphonobutanoic acid (L-AP4) following exposure to L-quisqualic acid (QUIS). We have examined the interaction of 43 structural analogues of L-AP4 with both the 'induction' site and the QUIS-sensitive AP4 site in rat hippocampus. The synthesis of cis- and trans-4-phosphonoxy-L-proline, 3-(RS)-amino-5-phosphonopentanoic acid and 2(RS)-amino-5-phenyl-4(RS)-phosphonopentanoic acid (gamma-benzyl AP4) are described. None of the test compounds interact with the induction site; thus L-QUIS remains the only compound known to induce this effect. However, one compound (L-2-amino-3-(5-tetrazolyl)-propanoic acid (L-aspartate tetrazole) 'pre-blocked' and reversed the effects of QUIS. In addition, the potency of 16 analogues increased more than 4-fold following exposure of slices to L-QUIS. Among these, L-AP4, L-AP5, 2-amino-4-(methylphosphino)butanoic acid (AMPB), and E-1(RS)-amino-3(RS)-phosphonocyclopentanecarboxylic acid (E-cyclopentyl AP4) displayed IC50 values of less than 0.100 mM after QUIS. The results presented here suggest that the QUIS-sensitive AP4 site requires a spatial configuration of functional groups similar to that present in E-cyclopentyl AP4. The presence of a primary amino group and a phosphorus-containing group (either monoanionic or dianionic) appear to be required, however, a carboxyl group is not essential for interaction. The pharmacology of the QUIS-sensitive AP4 site suggests that it is distinct from other known binding sites for L-AP4 in the central nervous system (CNS).

Aminobutyrates↗
PubMed1992

Activity of the conformationally rigid 2-amino-4-phosphonobutanoic acid (AP4) analogue (RS)-1-amino-3-(phosphonomethylene)cyclobutane-1-carboxylic acid (cyclobutylene AP5) on evoked responses in the perforant pathway of rat hippocampus.

The highly rigid and conformationally extended 2-amino-4-phosphonobutanoic acid (AP4) analogue (RS)-1-amino-3-(phosphonomethylene)-cyclobutane-1-carboxylic acid (cyclobutylene AP5) was synthesized and found to inhibit evoked responses in the rat lateral perforant path (LPP) with an IC50 of 41 (+/- 1.5 S.E.M.) microM and the medial perforant pathway with an IC50 of 218 (+/- 3.7 S.E.M.) microM. Furthermore, paired pulse potentiation experiments suggest that cyclobutylene AP5 acts, in part, at a presynaptic site in the LPP. Thus, cyclobutylene AP5 appears to act in a similar manner to L-AP4 in the perforant pathway. These data support the hypothesis that L-AP4 assumes an extended conformation at the L-AP4 receptor of the LPP.

Animals↗
PubMed1991

Characterization of retinal and hippocampal L-AP4 receptors using conformationally constrained AP4 analogues.

In the past, the absence of useful 2-amino-4-phosphonobutanoic acid (AP4) analogues has hampered the pharmacological study and comparison of different systems which are sensitive to L-AP4. Several conformationally constrained AP4 analogues have now been synthesized: (E)- and (Z)-1-amino-3-phosphonocyclopentanecarboxylic acid [(E)- and (Z)-cyclopentyl AP4], and (E)- and (Z)-1-amino-3-phosphonocyclohexanecarboxylic acid [(E)- and (Z)-cyclohexyl AP4], and the recently synthesized cyclopropyl analogues (E)- and (Z)-2-amino-2,3-methano-4-phosphonobutanoic acid [(E)- and (Z)-cyclopropyl AP4]. Therefore, we have examined and report here the pharmacology of two retinal and two hippocampal L-AP4 sensitive systems using these analogues. In addition, the pharmacology of two kainic acid/alpha-amino-3-hydroxy-5-methylisoxazole-4- propionic acid (KAIN/AMPA) pathways and one N-methyl-D-aspartate (NMDA) hippocampal pathway was examined. We found that the rank order potency of the L-AP4 sensitive systems were similar though not identical. The KAIN/AMPA and NMDA systems had a quite different rank order of potencies than the L-AP4 systems. These data suggest that the L-AP4 receptors in these different systems are structurally similar to each other and differ from both KAIN/AMPA and NMDA receptors.

Aminobutyrates↗
PubMed1991

NMDA-, kainate- and quisqualate-stimulated release of taurine from electrophysiologically monitored rat hippocampal slices.

While excitatory amino acids (EAAs) are known to evoke the release of taurine in the hippocampus, we have found that taurine is localized primarily in dendrites and only to a lesser extent in terminals in this region. To determine whether taurine is released as a neurotransmitter by non-toxic concentrations of EAAs, or exclusively as a neuroprotectant in response to excitotoxicity, we monitored the release of amino acids from hippocampal slices during simultaneous electrophysiological recording in the CA1 region to assess tissue viability. N-methyl-D-aspartate (NMDA) was the most potent of the EAA agonists tested for stimulating release of taurine. Exposure of slices to 120 microM NMDA increased the concentration of taurine in the perfusate to 1325% of its basal value. Kainate (KA) at a concentration of 128 microM increased taurine to 543% of baseline while quisqualate (Quis) at a concentration of 120 microM increase taurine to only 202% of its baseline value. Release of taurine in response to NMDA and KA peaked during the period when the concentration of the agonist was declining in the bath and did not return to its baseline value until 20 min after removal of the agonist. Increases in release of taurine were associated with concentrations of NMDA, KA, and Quis that caused an incomplete recovery of the CA1 field potential. These results suggest that taurine is primarily released by concentrations of glutamate receptor agonists that exhibit evidence of excitotoxicity in the CA1 region.

Animals↗
PubMed1991

Pre-exposure to L-homocysteinesulfinic acid blocks quisqualate-induced sensitization to L-2-amino-4-phosphonobutanoic acid.

Quisqualic acid sensitizes hippocampal CA1 neurons to depolarization by L-2-amino-4-phosphonobutanoic acid (L-AP4). This sensitization to L-AP4 is known to be blocked by simultaneous exposure to L-homocysteinesulfinic acid, L-alpha-aminoadipic acid and L-serine-O-sulfate during exposure to quisqualate. We report here that these compounds also act as 'pre-blockers' which, when added and removed from the medium prior to exposure to quisqualate, prevent subsequent induction of sensitization to L-AP4 by quisqualate. This pre-blockade suggests that simple competitive inhibition of extracellular receptor or uptake sites may not be the mechanism by which these compounds attenuate the action of quisqualate in this 'Quis-effect'.

Action Potentials↗
PubMed1991

Synthesis of the 2-amino-4-phosphonobutanoic acid analogues (E)- and (Z)-2-amino-2,3-methano-4-phosphonobutanoic acid and their evaluation as inhibitors of hippocampal excitatory neurotransmission.

The cyclopropyl compounds (Z)- and (E)-2-amino-2,3-methano-4-phosphonobutanoic acid, 5 and 6, respectively, were prepared as constrained analogues of 2-amino-4-phosphonobutanoic acid (AP4), a selective glutamate receptor ligand. A Horner-Emmons reaction of trimethyl N-(benzyloxycarbonyl)phosphonoglycinate with 2-(diethoxyphosphinyl)acetaldehyde gave the protected dehydroamino acids 9 and 10, which were individually subjected to the following sequence of reactions: cycloaddition of diazomethane, photoelimination of N2, and acid hydrolysis, to give 5 and 6, respectively. Extracellular recording techniques were used to evaluate the abilities of 5 and 6 to block evoked synaptic transmission in specific neuronal pathways of the rat hippocampal slice. In the lateral perforant path (LPP) 5 and 6 were equipotent and possessed IC50 values of 18 and 17 microM, respectively. In the medial perforant path (MPP), 6 (IC50 = 81 microM) was much more potent than 5 (IC50 = 1580 microM). In paired pulse experiments which differentiate presynaptic and postsynaptic inhibition, 5 and 6 enhanced the second response to the same extent as L-AP4, suggesting a presynaptic site of action for these compounds. In contrast, the cyclopentyl AP4 analogues 3 and 4 enhanced the second response to a lesser extent. It was concluded that the biologically active conformation of AP4 in the LPP is different than in the MPP. In order to explain the same potency of 5 and 6 in the LPP, it was postulated that the two analogues assume a conformation that allows their functional groups to occupy the same relative place in space. Molecular modeling showed that the best overlap was achieved when the alpha C-beta C-gamma C-P dihedral angle for 5 was in the range of 130 degrees to 180 degrees and that of 6 was in the range of -130 degrees to -180 degrees. The results suggest that the bioactive conformation of AP4 in the LPP is an extended one.

Aminobutyrates↗
PubMed1990

Synthesis of acyclic and dehydroaspartic acid analogues of Ac-Asp-Glu-OH and their inhibition of rat brain N-acetylated alpha-linked acidic dipeptidase (NAALA dipeptidase).

The following structural and conformationally constrained analogues of Ac-Asp-Glu-OH (1) were synthesized: Ac-Glu-Glu-OH (2), Ac-D-Asp-Glu-OH (3), Ac-Glu-Asp-OH (4), Ac-Asp-Asp-OH (5), Ac-Asp-3-aminohexanedioic acid (6), Ac-3-amino-3-(carboxymethyl)propanoyl-Glu-OH (7), N-succinyl-Glu-OH (8), N-maleyl-Glu-OH (9), N-fumaryl-Glu-OH (10), and Ac-delta ZAsp-Glu-OH (11). These analogues were evaluated for their ability to inhibit the hydrolysis of Ac-Asp-[3,4-3H]-Glu-OH by N-acetylated alpha-linked acidic dipeptidase (NAALA dipeptidase) in order to gain some insight into the structural requirements for the inhibition of this enzyme. Analogues 4-6 and 9 were very weak inhibitors of NAALA dipeptidase (Ki greater than 40 microM), while 2, 3, and 7 with Ki values ranging from 3.2-8.5 microM showed intermediate inhibitory activity. The most active inhibitors of NAALA dipeptidase were compounds 8, 10, and 11 with Ki values of 0.9, 0.4, and 1.4 microM, respectively. These results suggest that the relative spacing between the side chain carboxyl and the alpha-carboxyl group of the C-terminal residue may be important for binding to the active site of the enzyme. They also indicate that the chi 1 torsional angle for the aspartyl residue is in the vicinity of 0 degrees.

Animals↗
PubMed1989

High-affinity transport of L-glutamine by a plasma membrane preparation from rat brain.

Plasma membrane vesicles prepared from rat brain contain a saturable, high-affinity transport system for L-glutamine that exhibits the following characteristics: (1) The rate of L-glutamine transport is linear up to 200 micrograms/mL membrane protein. (2) Transport of [3H]-L-glutamine is linear with time for at least 10 min, is significantly reduced by lowering the assay temperature to 4 degrees C, and is essentially abolished by the addition of excess unlabeled L-glutamine. (3) The transport rate is optimal in the range of pH 7.4-8.2. (4) The system exhibits a Km for L-glutamine of approximately 1.7 microM and a Vmax of approximately 46 pmol/(min.mg of protein). (5) The system is not highly dependent upon the addition of monovalent or divalent cations. (6) Inhibitor studies reveal that the amino acid amides exhibit the highest affinity for the system and that there is a high specificity for the L-isomers.

Amino Acids↗
PubMed1989

Novel recognition site for L-quisqualate sensitizes neurons to depolarization by L-2-amino-4-phosphonobutanoate (L-AP4).

Brief exposure of rat hippocampal slices to L-quisqualate sensitizes pyramidal neurons to depolarization by L-2-amino-4-phosphonobutanoate (L-AP4). We report here experiments designed to clarify the duration, pharmacology, mechanism, and pathway specificity of this 'QUIS-effect'. The quisqualate-induced sensitization to L-AP4 decreases only 3-fold over a 4 h period. No compound besides quisqualate has been found to induce the QUIS-effect, including quisqualate analogues, potent excitatory amino acid agonists, L-glutamate, L-aspartate, and compounds known to stimulate second messenger systems in hippocampal slices. Of 43 compounds assayed here, only 5 are able to block the induction of the QUIS-effect. Although these blockers are also potent ligands at a chloride-dependent glutamate uptake site, the marked difference in rank ordering of compounds for QUIS-effect blockade and uptake site potency suggests that the QUIS-effect is not induced through this uptake site. The QUIS-effect can be induced in the CA1 region, the medial perforant path, and the lateral olfactory tract of the rat, and in the guinea pig CA1. It cannot be induced in the L-AP4-sensitive rat lateral perforant path (LPP), suggesting that the receptors for L-AP4 in the LPP may be distinct from those that are sensitized by quisqualate in the other pathways.

Action Potentials↗
PubMed1989

An explanation for the purported excitation of piriform cortical neurons by N-acetyl-L-aspartyl-L-glutamic acid (NAAG).

The excitation of piriform cortical neurons by iontophoresis of N-acetyl-L-aspartyl-L-glutamic acid (NAAG) isolated from rat brain is frequently cited as major support for the possible neurotransmitter role of NAAG in the CNS [ffrench-Mullen, J. M. H., Koller, K., Zaczek, R., Coyle, J. T., Hori, N. & Carpenter, D. O. (1985) Proc. Natl. Acad. Sci. USA 82, 3897-3900]. However, we have been unable to reproduce this observation using synthetic NAAG, and instead we offer an alternative explanation. In our experiments, iontophoresis of the sodium salt of synthetic NAAG did not induce single-unit spiking at sites in slices of rat piriform cortex that responded vigorously to L-glutamate. In contrast, iontophoresis of the potassium salt of synthetic NAAG or of potassium ions alone induced single unit activity. The responses to both NAAG/KCl and KCl alone were inhibited by L-2-amino-4-phosphonobutanoic acid and desensitized rapidly, as previously reported for NAAG. These results suggest that residual potassium ions, remaining after the original purification of NAAG, were responsible for the excitations attributed to NAAG.

Animals↗
PubMed1979

Protein induced by bacteriophage T4 which is absent in Escherichia coli infected with nuclear disruption-deficient phage mutants.

A protein induced by wild-type T4 phage which is absent in Escherichia coli infected with nuclear disruption-deficient phage (with mutations in gene ndd) was identified by polacrylamide gel electrophoresis. This protein was synthesized at maximum rate at 3 to 6 min after infection. It had a molecular weight of 15,000 determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It was associated with sedimentable fractions of the cell from which it can be dissociated with 1 M guanidine-hydrochloride. The dissociated protein can be partly recovered in a form soluble in dilute buffer after partial purification and dialysis. The occurrence of this protein in a particulate cell fraction is of interest because of the postulated role of the bacterial cell membrane in nuclear disruption.

Coliphages↗
PubMed1976

Identification and preliminary characterization of a mutant defective in the bacteriophage T4-induced unfolding of the Escherichia coli nucleoid.

The nucleoids of Escherichia coli S/6/5 cells are rapidly unfolded at about 3 min after infection with wild-type T4 bacteriophage or with nuclear disruption deficient, host DNA degradation-deficient multiple mutants of phage T4. Unfolding does not occur after infection with T4 phage ghosts. Experiments using chloramphenicol to inhibit protein synthesis indicate that the T4-induced unfolding of the E. coli chromosomes is dependent on the presence of one or more protein synthesized between 2 and 3 min after infection. A mutant of phage T4 has been isolated which fails to induce this early unfolding of the host nucleoids. This mutant has been termed "unfoldase deficient" (unf-) despite the fact that the function of the gene product defective in this strain is not yet known. Mapping experiments indicate that the unf- mutation is located near gene 63 between genes 31 and 63. The folded genomes of E. coli S/6/5 cells remain essentially intact (2,000-3,000S) at 5 min after infection with unfoldase-, nuclear disruption-, and host DNA degradation-deficient T4 phage. Nuclear disruption occurs normally after infection with unfoldase- and host DNA degradation-deficient but nuclear disruption-proficient (ndd+), T4 phage. The host chromosomes remain partially folded (1,200-1,800S) at 5 min after infection with the unfoldase single mutant unf39 x 5 or an unfoldase- and host DNA degradation-deficient, but nuclear disruption-proficient, T4 strain. The presence of the unfoldase mutation causes a slight delay in host DNA degradation in the presence of nuclear disruption but has no effect on the rate of host DNA degradation in the absence of nuclear disruption. Its presence in nuclear disruption- and host DNA degradation-deficient multiple mutants does not alter the shutoff to host DNA or protein synthesis.

Adsorption↗