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K M Johnson

Publications and source records attributed to K M Johnson.

At least 145 records · Page 8Linked to original sources
PubMed1989

Effects of nicotinic agonists and antagonists on N-methyl-D-aspartate-induced 3H-norepinephrine release and 3H-(1-[1-(2-thienyl)cyclohexyl]-piperidine) binding in rat hippocampus.

The nicotinic agonists dimethylphenylpiperazinium iodide (DMPP) and carbachol (CARB) as well as (-)nicotine [-)NIC) were tested alone and in combination with N-methyl-D-aspartate (NMDA) for their abilities to enhance the efflux of 3H-norepinephrine (NE) from slices of rat hippocampus. CARB and (-)NIC produced small, transient increases in NE efflux, while DMPP produced larger, longlasting increases. Inasmuch as the nicotinic antagonists mecamylamine (MECA) and hexamethonium (C6) did not consistently inhibit the increases in NE efflux produced by these agonists, the role of a nicotinic receptor in mediating these responses is uncertain. CARB and DMPP enhanced the ability of NMDA to stimulate NE release, while (-)NIC did not. MECA, but not C6, was found to selectively antagonize NMDA-stimulated NE release that did not appear to involve a nicotinic receptor. Binding studies indicated that MECA and the related nicotinic antagonist pempidine produced an inhibition of NMDA-stimulated NE release by an action at the PCP receptor that is known to be linked to the NMDA receptor-ionophore complex. These data suggest that the actions of these ganglionic blocking agents on excitatory responses in the hippocampus involve inhibition of excitatory amino acid as well as nicotinic receptors.

Animals↗
PubMed1989

Effects of amygdaloid kindling on NMDA receptor function and regulation.

These studies were conducted to determine whether amygdaloid kindling results in the long-term alteration of NMDA receptors which could explain the persistent reduction in seizure threshold seen in this phenomenon. NMDA-induced [3H]norepinephrine (NE) release, NMDA-sensitive L-[3H]glutamate binding, and NMDA and glycine-enhanced [3H]TCP binding were measured in brain tissue from kindled rats and nonstimulated control rats 3 to 6 weeks after the last seizure. There was no difference in the ability of NMDA to induce [3H]NE release from kindled or control slices of amygdala or hippocampus. There was also no difference in the ability of phencyclidine (PCP) or Mg2+ to inhibit [3H]NE release induced by 100 microM NMDA. Equilibrium saturation experiments of NMDA-sensitive L-[3H]glutamate binding revealed no differences in KD or Bmax values between control and kindled cortex, amygdala, and hippocampus. The Ki values for NMDA displacement of L-[3H]glutamate binding also did not differ in kindled tissue. NMDA-enhanced [3H]TCP binding was similar in cortex, amygdala, and hippocampus of kindled and control tissues. Finally, glycine-enhanced [3H]TCP binding was not different in control or kindled tissues. These studies suggest that the NMDA recognition site and the modulation of the NMDA receptor/ion channel complex by magnesium, PCP, and glycine are not altered several weeks after the last seizure. Even though NMDA-mediated electrophysiological responses are reportedly enhanced in kindled tissue at that time, the mechanism(s) underlying the enhancement remains to be determined.

Amygdala↗
PubMed1989

Characterization of the binding of radioligands to the N-methyl-D-aspartate, phencyclidine, and glycine receptors in buffy coat membranes.

Rapid vacuum filtration assays were used to quantitate radioligand binding to phencyclidine (PCP), N-methyl-D-aspartate (NMDA), and strychnine-insensitive glycine receptors in a simple buffy coat preparation of rat cortical membranes. KD and Bmax values for [3H]glycine binding were very similar to those previously reported by workers who used centrifugation for the separation of free and bound [3H]glycine. We also found that this preparation had a high percentage of NMDA-displaceable L-[3H]glutamate binding sites, which demonstrated a pharmacology very similar to that previously observed in more purified synaptic plasma membranes. Hill analysis of the displacement curves indicated that glutamate bound to a single class of sites, but that NMDA and NMDA antagonists may interact with this site in a negatively cooperative fashion. This preparation was also found to be suitable for the study of NMDA and glycine receptor regulation of the associated ion channel, as these effectors, alone and in combination, increased the affinity with which [3H]TCP bound to the PCP receptor believed to be located within the ion channel. Thus, the ability to measure radioligand binding to these three sites in the same simple membrane preparation should greatly facilitate the study of the interaction between them.

Animals↗
PubMed1989

Effects of the halothane-sensitivity gene on sarcoplasmic reticulum function.

Pigs heterozygous for the halothane-sensitivity gene exhibit a distinct phenotype with regard to both in vivo and in vitro muscle responses to halothane (E. M. Gallant, J. R. Mickelson, B. D. Roggow, S. K. Donaldson, C. F. Louis, and W. E. Rempel. Am. J. Physiol. 257 (Cell Physiol. 26): C781-C786, 1989). In this paper heavy sarcoplasmic reticulum (SR) preparations were isolated from the muscles of pigs of all three genotypes. The rate of calcium release from SR of pigs homozygous for the halothane-sensitivity gene was approximately twice that of SR from pigs homozygous for the normal allele. Furthermore, in the presence of 6 microM Ca2+, the binding of [3H]ryanodine to SR isolated from the homozygous halothane-sensitive pigs was of a higher affinity than was the binding to SR isolated from the homozygous normal pigs (Kd = 70-90 vs. 265 nM, respectively). The SR from pigs heterozygous for the halothane-sensitivity gene, however, demonstrated intermediate values for the rate of calcium release and the affinity for [3H]ryanodine (Kd = 192 nM). Thus the alterations in heavy SR calcium release and [3H]ryanodine binding in the pigs containing one copy of the halothane-sensitivity gene demonstrate a distinct heterozygote phenotype. These data also suggest that the protein product of this gene is closely associated with, and perhaps identical to, the SR calcium release channel-ryanodine receptor protein.

Adenosine Triphosphate↗
PubMed1989

Spermine enhances binding to the glycine site associated with the N-methyl-D-aspartate receptor complex.

Spermine enhanced strychnine-insensitive [3H]glycine binding 3-fold with an EC50 of 27 +/- 3.1 microM. Spermidine and putrescine were without effect, whereas the ethylenediamine analog of spermine had an intermediate effect. Eadie-Hofstee analysis revealed that spermine increased the affinity of glycine for its receptor without a significant change in receptor density. This effect persisted in the presence of glycine or N-methyl-D-aspartate receptor antagonists. Furthermore, spermine produced a leftward shift in the IC50 of glycine agonists in displacing [3H]glycine binding, without altering the IC50 for glycine antagonists. These data indicate that spermine interacts with the glycine receptor through a novel binding site and, further, that spermine can be used to discriminate glycine agonist and antagonist binding.

Animals↗
PubMed1989

Effects of acute and chronic clozapine and haloperidol on in vitro release of acetylcholine and dopamine from striatum and nucleus accumbens.

The purpose of this investigation was to determine if striatal or nucleus accumbens dopamine (DA) release, ACh release or DA receptor function were altered by acute and chronic haloperidol or clozapine treatment in a manner consistent with the reported pharmacological effects of each drug on A9 and A10 DA cell bodies and projection areas, when experiments were performed without a drug-free, or washout, period after drug treatment. The release of neurotransmitters reported here was evaluated using a slice-superfusion assay system. Transmitter release was induced either by an electrical field (for DA and ACh) or by application of either amphetamine or amfonelic acid (DA only). Dopaminergic receptor function was assessed by inhibiting electrically stimulated ACh release with in vitro TL-99 (a dopaminergic agonist) and by reversing that inhibition with in vitro neuroleptics or with ex vivo experimental paradigms (the in vitro analysis of transmitter release subsequent to in vivo drug administration). These data suggest that although there are differences between haloperidol and clozapine, there is no difference between the degree of postsynaptic DA receptor blockade produced that can be attributed to the duration of neuroleptic treatment. Chronic clozapine (20 mg/kg x 21 days) reversed TL-99-induced inhibition of ACh release in the nucleus accumbens only, whereas chronic haloperidol (0.5 mg/kg x 21 days) produced a similar reversal in both brain areas. One possible explanation for the lack of effect of chronic clozapine treatment in the striatum is that carrier-mediated (amphetamine-stimulated) DA release is enhanced in the striatum but not in the nucleus accumbens, suggesting that the potential DA receptor block in the striatum may be compromised by enhanced striatal DA levels. Acute haloperidol (0.5 mg/kg) was found to increase electrically stimulated ACh release in the striatum and DA release in the nucleus accumbens. Tolerance developed in the striatum, but not the nucleus accumbens, with repeated administration. However, acute clozapine had no effect on ACh release in either area, but it was found to enhance DA release in the striatum, an effect to which tolerance developed with chronic administration. Further, comparison of these data with data obtained using haloperidol and clozapine in vitro suggests that it is unlikely that these effects are due to residual drug still present in these tissues at the time of experimentation. These data are discussed with regard to electrophysiological and pharmacological differences observed between clozapine and haloperidol on the activity of A9 and A10 DA cells after chronic neuroleptic treatment.

Acetylcholine↗
PubMed1988

Structural requirements for activation of the glycine receptor that modulates the N-methyl-D-aspartate operated ion channel.

It has recently been demonstrated that glycine can potentiate several measures of N-methyl-D-aspartate (NMDA)-induced channel opening, including radioligand binding to the PCP receptor. These data suggest that the NMDA/PCP receptor complex may be allosterically modulated by a binding site for glycine. We report here that several other monocarboxylic amino acids enhance NMDA-induced [3H]TCP binding and displace [3H]glycine binding with similar apparent affinities and stereoisomerism. The results are discussed with relation to the structural requirements for compounds to bind to this site.

Amino Acids↗
PubMed1988

Equilibrium analysis of [3H]TCP binding: effects of glycine, magnesium and N-methyl-D-aspartate agonists.

It has been reported that glutamate can increase the binding of [3H]TCP to phencyclidine (PCP) receptors by an action on receptors which are selective for N-methyl-D-aspartate (NMDA). Recently this laboratory has reported that glycine and magnesium can amplify this effect of NMDA agonists in well-washed, lysed cortical membranes. Here we report that maximally effective concentrations of glutamate (10 microM), NMDA (300 microM), MgCl2 (300 microM) and glycine (10 microM) increase the affinity of the PCP receptor for [3H]TCP by approximately 4-fold in the absence of any change in the density of PCP receptors. However, in combination with glutamate, magnesium had the further effect of increasing the Bmax by about 75%. Finally, a synaptosomal P2 preparation, which had not been washed to minimize the concentration of endogenous effectors had a Bmax value similar to the well-washed preparation, but had a KD value 8-fold lower. These data indicate that the primary effect of NMDA agonists, glycine, and low concentrations of magnesium ions is to convert the PCP receptor from a low-affinity to a high-affinity state. These data are discussed in relation to the functional regulation of the NMDA ionophore.

Animals↗
PubMed1988

Abnormal sarcoplasmic reticulum ryanodine receptor in malignant hyperthermia.

Previous studies have demonstrated that skeletal muscle from individuals susceptible to malignant hyperthermia (MH) has a defect associated with the mechanism of calcium release from its intracellular storage sites in the sarcoplasmic reticulum (SR). In this report we demonstrate that the [3H]ryanodine receptor of isolated MH-susceptible (MHS) porcine heavy SR exhibits an altered Ca2+ dependence of [3H]ryanodine binding at the low affinity Ca2+ site as well as a lower Kd for ryanodine (92 versus 265 nM) when compared to normal porcine SR. The Bmax of the normal and MHS [3H] ryanodine receptor (9.3-12.6 pmol/mg) was not significantly different, and analysis of MHS and normal SR proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis did not reveal a significant difference in the intensity of Coomassie Blue staining of the spanning protein/ryanodine receptor region of the gels (Mr greater than 300,000). We also find that MHS porcine muscle intact fiber bundles exhibit a 5-10-fold lower ryanodine threshold for twitch and tetanus inhibition, and contracture onset when compared to normal muscle. Since the SR ryanodine receptor is a calcium release channel as well as a component intimately involved in transverse tubule-SR communication, abnormalities in the skeletal muscle ryanodine receptor may be responsible for the abnormal SR calcium release and contractile properties demonstrated by MHS muscle.

Alkaloids↗
PubMed1988

Linkage between phencyclidine (PCP) and N-methyl-D-aspartate (NMDA) receptors in the cerebellum.

It has been suggested that phencyclidine (PCP) receptors may not be linked with N-methyl-D-aspartate (NMDA) receptors in all brain areas. We found that NMDA enhanced [3H]TCP (a PCP analog) binding in extensively washed cortical, but not cerebellar membranes. However, PCP potently inhibited NMDA-induced [3H]norepinephrine release from cerebellar slices in a concentration-dependent manner, suggesting that a subtype of cerebellar PCP receptors is functionally linked with NMDA receptors. It is suggested that this subtype cannot be demonstrated by [3H]TCP binding because of the predominance of low affinity PCP receptors in the cerebellum.

Animals↗
PubMed1988

Calcium ionophore enhances the electron spin resonance signal from isolated skeletal muscle.

Electron spin resonance studies of the free radical signal from isolated skeletal muscle during experimental damage have shown that elevation of muscle intracellular calcium with the calcium ionophore A23187 induced an average 61% increase in the amplitude of the signal of g value 2.0047 compared to paired, untreated control muscles, accompanied by a large efflux of intracellular creatine kinase to the external medium. Inhibitors of the calcium-induced loss of cell viability leading to enzyme efflux, i.e., chlorpromazine, phenidone and nordihydroguaiaretic acid had variable effects on the signal, suggesting that the free radical signal obtained from skeletal muscle by electron spin resonance techniques is stimulated by intracellular calcium overload, but is not directly related to the mechanisms by which calcium overload leads to a loss of cell viability leading to intracellular enzyme efflux.

Animals↗
PubMed1988

Comparison of the effects of MK-801 and phencyclidine on catecholamine uptake and NMDA-induced norepinephrine release.

MK-801 was found to be more potent than phencyclidine (PCP) as an inhibitor of N-methyl-D-aspartate-induced [3H]norepinephrine (NE) release and [3H]TCP binding in the hippocampus. On the other hand, MK-801 was slightly less potent than PCP to enhance kainate-stimulated [3H]NE release and to inhibit hippocampal [3H]NE uptake. Further, MK-801 was strikingly less potent than PCP as an inhibitor of striatal synaptosomal [3H]dopamine uptake. These data are discussed with reference to the therapeutic potential of MK-801.

Animals↗
PubMed1988

Hyperinflation of the lungs in infants with large left-to-right shunts.

Infants with significant left-to-right shunts due to ventricular septal defects and atrioventricular canal defects commonly present with respiratory symptoms, such as shortness of breath while feeding, tachypnea, and wheezing. Radiographs show hyperinflated lungs as well as cardiomegaly and increased vascularity. Enlarged vessels adjacent to small compressible airways as well as peribronchial interstitial edema may cause diffuse air trapping. In this study, using an automated planimetric device, we measured the total thoracic, cardiomediastinal, and lung volumes in a group of patients with large left-to-right shunts as well as in a group of normal controls and found that, as expected, all volumes were significantly increased in the abnormal group. We also tried to correlate these volumes (corrected for patient size) with the degree of left-to-right shunt and found that there was no significant correlation between the cardiac or lung volumes and shunt size as estimated by cardiac catheterization.

Heart Septal Defects↗
PubMed1987

Glycine potentiates N-methyl-D-aspartate-induced [3H]TCP binding to rat cortical membranes.

In extensively washed preparations of rat cortical membranes, N-methyl-D-aspartate (NMDA) increases the specific binding of [3H]TCP by over 4-fold in a concentration dependent manner (EC50 = 3.1 microM). Glycine (1 microM) potentiates the maximal effect of NMDA by a factor of 1.7. The effect of glycine is concentration dependent (EC50 = 380 nM) and strychnine insensitive. These data are discussed with reference to the recently reported effects of glycine on the NMDA operated cation channel and the relationship between the PCP and NMDA receptors.

Animals↗
PubMed1987

Phencyclidine (PCP)-like inhibition of N-methyl-D-aspartate-evoked striatal acetylcholine release, H-TCP binding and synaptosomal dopamine uptake by metaphit, a proposed PCP receptor acylator.

The phencyclidine (PCP) receptor acylator, metaphit, has been reported to act as a PCP antagonist. Recent electrophysiological and behavioral assessments of metaphit action have revealed, however, that this compound can also act as a PCP-like agonist. The present study examined the effects of metaphit on the inhibition of N-methyl-D-aspartate (NMDA)-induced 3H-acetylcholine (ACh) release, 3H-TCP binding and synaptosomal 3H-dopamine (DA) uptake in the rat striatum. Preincubation of striatal slices for 10 min in the presence of metaphit, followed by a prolonged washout, produced a concentration-dependent inhibition of the ACh release evoked by 300 microM NMDA. At high concentrations, preincubation with PCP also resulted in inhibition of this measure. However, this could be reduced by extending the washout period, a procedure which had no effect on the inhibition produced by metaphit. At 10 microM, metaphit resulted in a 53% reduction in NMDA-evoked ACh release while PCP had no effect under identical conditions. Preincubation of slices in 10 microM PCP and metaphit reduced the metaphit inhibition by 62%. The effects of PCP and metaphit, alone or in combination, on NMDA-induced ACh release were paralleled by a loss of 3H-TCP binding sites in striatal tissue incubated under identical conditions suggesting that metaphit exerts long-lasting agonist-like actions on PCP receptors coupled to NMDA receptors. Although these results do not explain the ability of metaphit to antagonize PCP effects in other assays, we did observe that preincubation of striatal synaptosomes with metaphit also resulted in an irreversible inhibition of 3H-DA uptake. These data are discussed in relation to the interaction of metaphit with PCP receptors in various systems.

Acetylcholine↗
PubMed1987

Inhibition of N-methyl-D-aspartate-induced hippocampal [3H]norepinephrine release by phencyclidine is dependent on potassium concentration.

This study examined the ability of phencyclidine (PCP) to inhibit the responses to N-methyl-D-aspartate (NMDA) in depolarizing concentrations of K+. The effects of PCP and Mg2+ on NMDA-induced norepinephrine release from hippocampal slices were measured during superfusion with various extracellular concentrations of K+. The IC50 values for Mg2+ and PCP were significantly higher in K+ concentrations above 6 mM. These data are supportive of the hypothesis that PCP produces a voltage-dependent blockade of NMDA-activated ion channels.

2-Amino-5-phosphonovalerate↗
PubMed1987

An endogenous ligand of the brain sigma/PCP receptor antagonizes NMDA-induced neurotransmitter release.

The present study provides evidence for the presence of an endogenous ligand for the phencyclidine (PCP) receptor of mammalian brain. Partially purified bovine hippocampal extracts potently and dose dependently inhibit binding to PCP receptors of [3H]N-(1-[2-thienyl]-cyclohexyl)piperidine (TCP), a highly potent and specific ligand of PCP receptors. In addition to demonstrating PCP-like binding properties, the partially purified extract mimics biological actions of PCP upon neurotransmitter release. HPLC fractions active in the [3]TCP binding assay, by contrast to fractions inactive in the binding assay, potently elicited stimulation of spontaneous acetylcholine and dopamine efflux and inhibited NMDA-stimulated release of acetylcholine and dopamine. The transmitter release assay provides validation of a PCP-like physiological activity exerted by bovine hippocampal extracts partially purified by HPLC.

Acetylcholine↗