Binding sites for a peripheral type benzodiazepine antagonist ([3H]PK 11195) in human iris

Peripheral-type benzodiazepine receptors

Since their first description as anomalous high affinity diazepam binding sites in rat peripheral tissues, the peripheral-type benzodiazepine receptor (PBR) has been increasingly studied to better understand nonneural effects of the benzodiazepines. The mammalian PBR is ubiquitously distributed with high concentrations in the outer mitochondrial membrane of secretory tissues. In regions of the brain, the density of PBR can equal or exceed the density of central-type benzodiazepine receptors. High affinity PK 11195 binding is diagnostic for the receptor while the affinity for benzodiazepines is species dependent. Recent cDNA cloning of a PBR component, the isoquinoline binding protein (IBP), shows no apparent sequence homology with any GABAA receptor subunits known to comprise central benzodiazepine receptor subtypes. The PBR seems at best only distantly related to CBRs. Recent advances in the pharmacology, biochemistry and molecular biology of the PBR are reviewed.

Altered peripheral benzodiazepine receptor density in human granulosa-lutein cells in relation to follicular maturity

Since the introduction of treatment by in vitro fertilization/embryo transfer (IVF-ET) in humans, a harmless approach to identifying the ovum with a greater chance of producing an implantable embryo has been sought worldwide. Our previous studies indicated a high correlation between degree of follicular maturation and benzodiazepine (BZ) receptor density in rats. We hypothesized that if such a correlation existed in humans, the latter might be used to evaluate degree of follicular maturation and, consequently, its corresponding oocyte competence. We used [3H]PK 11195, a ligand selective to peripheral BZ receptors, to determine their density in human granulosa-lutein (G-L) cells. [3H]PK 11195 bound to G-L cells with high affinity in a saturable manner. Scatchard analysis revealed the presence of a single population of receptors. The average equilibrium dissociation constant and maximal number of receptors (Bmax) measured in G-L cells were 3.4 +/- 0.2 nM and 608 +/- 61 fmol/mg protein, respectively. In G-L cells obtained from individual follicles, a significant increase in the specific binding to peripheral BZ receptors was noted in G-L cells of follicles yielding oocytes at an advanced stage of cumulus maturation or oocytes competent for fertilization and subsequent cleavage. When G-L cells were pooled from all the follicles of each individual woman, the average Bmax value of [3H]PK 11195 in G-L cells was 900 +/- 127 fmol/mg protein in women who conceived, which was 80% higher (P less than 0.01) than in women who did not conceive.(ABSTRACT TRUNCATED AT 250 WORDS)

Peripheral-type benzodiazepine receptors in human cerebral cortex, kidney, and colon

The specific binding of [3H]PK 11195 and [3H]Ro 5-4864 to human cerebral cortex, kidney, and colon membranes was studied in order to determine whether peripheral type benzodiazepine receptors (PBR) characteristics located in human tissues are similar to those located in calf or rat tissues. While [3H]PK 11195 (0.05-10 nM, final concentration) bound with high affinity (KD about 2 nM) to human cerebral cortex, kidney, and colon membranes, yielding maximal numbers of binding sites of 255 +/- 23, 1908 +/- 28, and 1633 +/- 98 fmol/mg protein, respectively, the specific binding of [3H]Ro 5-4864 (1.25-40 nM, final concentration), was barely detectable (nonspecific binding about 90% of the total binding). Furthermore, unlabeled PK 11195 was two orders of magnitude more potent than unlabeled Ro 5-4864 in displacing [3H]PK 11195 specific binding from human cerebral cortex and kidney membranes. These results indicate that PBR binding characteristics located in human tissues are similar (but not identical) to those located in calf tissues, but not to those located in rat tissues.

Benzodiazepines and the mammalian retina. I. Autoradiographic localisation of receptor sites and the lack of effect on the electroretinogram

The majority of specific benzodiazepine binding sites were found to be restricted to the innerplexiform layer of the rat retina, although there were minor amounts of binding in the inner nuclear and ganglion cell layers. Relatively high levels of non-specific benzodiazepine binding sites were, on the other hand, found in the pigment epithelium and ciliary body, as well as in the corneal epithelium. The specific binding was enhanced by the GABA-A agonist, muscimol. In both rats and cats, neither acute nor chronic administration of benzodiazepines or their antagonists altered the retinal functions, as determined by the electroretinogram. These results suggest that retinal benzodiazepine receptors do not influence visually induced preganglionic retinal activity.

Presence of peripheral-type benzodiazepine binding sites on human erythrocyte membranes

A nanomolar affinity peripheral-type benzodiazepine binding site is described in human erythrocyte membranes. [3H]PK 11195 is displaced from this binding site by unlabeled drugs with the rank order PK 11195 greater than Ro 5-4864 greater than flunitrazepam much greater than clonazepam. Neither GABA nor a non-hydrolyzable analog of GTP have an effect on binding parameters. These data provide evidence that a peripheral-type benzodiazepine binding site, pharmacologically similar to the intracellular binding site described in other tissues, is present in the plasma membrane of human erythrocytes.

Quantitative autoradiographic determination of binding sites for a peripheral benzodiazepine ligand ([3H]PK 11195) in human iris

Specific binding sites of peripheral-type benzodiazepines were investigated in human iris/ciliary body (8 eyes). Examination of color-coded prints and densitometric quantification of autoradiograms were performed on slides (20 micron) labelled with [3H]PK 11195 (1 nM) at 25 degrees C. Nonspecific binding was determined with PK 11211 (5 microM) or Ro 5-4864 (5 microM). Binding sites were present on all the slides, with equivalent density in the 3 regions of the preparation (ciliary body, iris, and pupil margin). The numbers of binding sites in ciliary body, iris, and pupil margin, respectively, were: 42.7 +/- 0.2, 30.1 +/- 0.5, and 37.4 +/- 0.4 femtomol/mg protein. Labelling on the pupil margin seemed to coincide with the iris sphincter muscle. The presence of peripheral benzodiazepine binding sites in iris muscular tissue, and particularly in the pupil margin, suggests that the iris preparation may be a valuable tool to detect putative physiological effects of peripheral benzodiazepines on muscular motility.