摘要:

AbstractInteractions of GABA, bicuculline methochloride and diazepam with [3H]TBOB binding to rat brain membranes were evaluated in vitro.GABA displaced [3H]TBOB binding with and IC50of 4μM and a slope factor near unity. The competitive GABA antagonist bicuculline methochloride shifted the displacement curve of GABA parallelly to the right, indicating that the interaction of GABA with [3H]TBOB binding is of an allosteric nature.In the presence of GABA, diazepam displaced the binding of [3H]TBOB according to a two-site model: a high affinity site with an IC50of about 50 nM and a lower affinity site with an IC50of about 30μM. Bicuculline methochloride abolished the nanomolar displacement by diazepam and increased the micromolar IC50value. These results indicate that the interaction of the high affinity diazepam site with the [3H]TBOB binding site is totally GABA dependent and that the low affinity effect of diazepam on [3H]TBOB binding is at least partially GABA dependent.It is likely that the low affinity potency of diazepam to displace [3H]TBOB binding has physiological relevance.

ISSN:1079-9893    

DOI:10.3109/10799899509049857

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

AbstractIt is generally accepted that the phospholipid and calcium-dependent enzyme protein kinase C (PKC) plays a significant role in secretion of hormones from anterior piuitary cells. The present study was undertaken to study age and sex-related changes in1. levels of immunoreactivity of PKC isozymes and2. distribution of immunoreactivity of PKC isozymes after stimulation with substance P (SP) in rat lactotroph-enriched cell cultures. Theα,β,δandζisozymes were present in both sexes and at all ages. There was a sex-specific differential regulation of the different PKC isozymes as a function of sexual maturation. In male rats there was an up-regulation of theαisozyme throughout the sexual development, while theβsubtype showed a small, but significant decrease in immunoreactivity with increasing age. In female rats, on the other hand, theβspecies was up-regulated with increasing age while the other subtypes remained constant. The concentration of theδandζisozymes was unaffected of sex and age. Stimulation of lactotroph-enriched cell cultures with substance P (SP) resulted in translocation of theαandβisozymes from the soluble to the particulate fraction while theδandζspecies were left unchanged independently of age and sex. However, a decrease in responsiveness was observed in adult male rats, although a significant degree of translocation ofαandβspecies was still detected. On the basis of these results it is suggested that in lactotroph-enriched cell cultures basal levels of PKC subtype immunoreactivity and distribution of immunoreactivity of PKC isozymes after SP challenge might be regulated as a function of sex and age.

ISSN:1079-9893    

DOI:10.3109/10799899509049858

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

AbstractWe have examined the effects of oxidizing and reducing agents on a number of subtypes of N-methyl-D-aspartate (NMDA) receptors expressed inXenopusoocytes. Oocytes were injected with cRNA for theε1 subunit from mouse to express homomeric receptors or withε1 in combination with eitherε1,ε2,ε3 orε4 subunits to express heteromeric receptors. All heteromeric combinations resulted in receptors that were affected by the redox reagents, dithiothreitol (DTT) and 5-5-dithio-bis-2-nitrobenzoic acid (DTNB). However, the effects on the small currents from homomeric receptors were quite variable. Theε1/ε3 combination showed a greater enhancement by DTT than any of the other combinations. All four receptors expressed showed both a component of persistent potentiation and a slowly reversible component. The reversible component was largest forε1/ε3. Additional experiments were done with S-nitrosocysteine (SNOC), a nitric oxide donor that may affect NMDA receptors by oxidation. SNOC had transient effects on the four heteromeric subunit combinations. The different sensitivities of particular subunit combinations may have pharmacological and clinical significance.

ISSN:1079-9893    

DOI:10.3109/10799899509049859

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

AbstractAMPA receptors may play an important role in acute and chronic neurodegenerative diseases. An assay for the specific binding of [3H]-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) to receptors in membranes from post-mortem human brain is described, which can be used in screening for selective AMPA receptor antagonists. Membranes were prepared from frozen human adult hippocampus and whole fetal brain tissues. [3H]-AMPA binding to human hippocampus was saturable; Scatchard analysis of equilibrium binding data indicated high and low affinity sites with affinity binding constants (KD) of 3.4±0.5 nM and 65±9 nM (n=7) respectively. Biphasic association and dissociation rate constants for [3H]-AMPA binding were consistent with the biphasic Scatchard analysis. Inhibition of [3H)-AMPA binding revealed a rank order of potency as quisqualate = AMPA>BOAA>L-glutamate = DNQX = CNQX>kainate>L-aspartate = NMDA. AMPA receptors in human fetal brain had a comparable pharmacology. AMPA/kainate receptors were expressed in frog oocytes following injection of RNA prepared from human fetal brain. Human brain tissues may therefore be utilized for screening and functional analysis of AMPA receptor antagonists.

ISSN:1079-9893    

DOI:10.3109/10799899509049860

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor