Diazepam binding of dissociated hippocampal cultures from fetal mice

Benzodiazepine binding studies on living cells: application of small ligands for fluorescence correlation spectroscopy

We demonstrate the applicability of fluorescence correlation spectroscopy (FCS) for receptor binding studies using low molecular weight ligands on the membranes of living nerve cells. The binding of the benzodiazepine Ro 7-1986/602 (N-des-diethyl-fluorazepam), labeled with the fluorophore Alexa 532, to the benzodiazepine receptor was analyzed quantitatively at the membrane of single rat hippocampal neurons. The values obtained for the dissociation constant Kd = (9.9 +/- 1.9) nm and the rate constant for ligand-receptor dissociation kdisS = (1.28 +/- 0.08) x 10(-3) s(-1) show that there is a specific and high affinity interaction between the dye-labeled ligand (Ro-Alexa) and the receptor site. The binding was saturated at approx. 100 nM and displacement of 10 nM Ro-Alexa, with a 1,000-fold excess of midazolam, showed a non-specific binding of 7-10%. Additionally, two populations of the benzodiazepine receptor that differed in their lateral mobility were detected in the membrane of rat neurons. The diffusion coefficients for these two populations [D(bound1) = (1.32 +/- 0.26) microm2/s; D(bound2) = (2.63 +/- 0.63) x 10(-2) microm2/s] are related to binding sites, which shows a mono-exponential decay in a time-dependent dissociation of the ligand-receptor complex.

Differentiation of a cell line from olfactory epithelium is induced by dibutyryladenosine 3',5'-cyclic monophosphate and 12-O-tetradecanoylphorbol-13-acetate

Olfactory receptor neurons undergo continual replacement with new cells differentiating from a population of basal cells located in the olfactory epithelium. We have previously described the isolation of a cell line from murine olfactory epithelium (MOE CL1) which is now shown to be sensitive to two differentiation promoting agents, dibutyryladenosine 3',5'-cyclic monophosphate (db-cAMP) and 12-O-tetradecanoylphorbol-13-acetate (TPA). Cells grown in the presence of db-cAMP or TPA, after a lag phase of 72-96 h, became bipolar, with long neurite-like processes. Cells conditioned for at least one passage in db-cAMP or TPA, or cells exposed to a mixture of db-cAMP and TPA, attained a bipolar morphology within 24 h. Cultures grown with db-cAMP, TPA or db-cAMP + TPA showed significant increases in the percentage of process-bearing cells. An increase in population doubling time and decrease in saturation density were also observed in cultures exposed to db-cAMP. Cells exposed to TPA continued to divide at the same rate as control cells, while those treated with db-cAMP + TPA underwent terminal differentiation. Peripheral-type benzodiazepine binding sites, which within the olfactory epithelium are localized on the receptor neurons, were present in homogenate membranes of undifferentiated cells. Cells differentiated by exposure to db-cAMP + TPA for 7 days showed a 65% increase in the density (Bmax) of peripheral-type benzodiazepine binding sites. Undifferentiated cells in control cultures showed no spontaneous changes in membrane potential or regenerative responses during current injection. Small, bipolar cells in morphologically differentiated cultures, however, were capable of generating several types of spontaneous changes in membrane potential including slow, regular oscillations; irregular, slow and fast depolarizations; and trains of action potentials.

Binding of [3H]Ro 5-4864 in primary cultures of astrocytes

Intact primary cultures of astrocytes display benzodiazepine receptors, which can be labeled with [3H]Ro 5-4864. Binding of [3H]Ro 5-4864 is specific, saturable and temperature dependent, being maximal at 0 degrees C. Scatchard analyses show a single population of high affinity binding sites with a Kd value of 6.7 nM and a Bmax value of congruent to 12,000 fmol/mg protein. The binding reaches equilibrium at congruent to 100 min, with k+1 of 0.0078 nM-1 X min-1 and is rapidly reversible with k-1 of 0.057 min-1. [3H]Ro 5-4864 binding is not modulated by GABA. Certain benzodiazepines (flunitrazepam, diazepam, Ro 7-3351) and dipyridamole displace this binding with IC50 values in the nanomolar range, whereas other benzodiazepines (alprazolam, clonazepam, chlordiazepoxide) as well as carbamazepine, phenytoin and phenobarbital have IC50 values in the micromolar range. These characteristics resemble those of Ro 5-4864 binding to brain membrane preparations reported by other authors and thus indicate that the cultured astrocytes are good models of their in vivo counterparts.

Flunitrazepam binding to intact and homogenized astrocytes and neurons in primary cultures

[3H]Flunitrazepam binds to intact and homogenized mouse astrocytes and neurons in primary cultures. In intact cells, the binding is to a single, high-affinity, saturable population of benzodiazepine binding sites with a KD of 7 nM and Bmax of 6,033 fmol/mg protein in astrocytic cells and a KD of 5 nM and Bmax of 924 fmol/mg protein in neurons. After homogenization, the Bmax values decrease drastically in both cell types, but most in astrocytes. The temperature and time dependency are different for the two cell types, with a faster association and dissociation in astrocytes than in neurons and a greater temperature sensitivity in the astrocytes. Moreover, flunitrazepam binding sites on neuronal and astrocytic cells have different pharmacological profiles. In intact astrocytic cells, Ro 5-4864 (Ki = 4 nM) is the most potent displacing compound, followed by diazepam (Ki = 6 nM) and clonazepam (Ki = 600 nM). In intact neurons, the relative order of potency of these three compounds is different: diazepam (Ki = 7 nM) is the most potent, followed by clonazepam (Ki = 26 nM) and Ro 5-4864, which has little effect. After homogenization the potency of diazepam decreases. We conclude that both neuronal and astrocytic cells possess high-affinity [3H]flunitrazepam binding sites. The pharmacological profile and kinetic characteristics differ between the two cell types and are further altered by homogenization.

Properties of [3H]diazepam binding sites on cultured murine glia and neurons

[3H]Diazepam binding was assayed in situ on living cultures of fetal mouse cerebral cortex or glia in an attempt to further characterize the high and low affinity binding sites. Mixed neuronal-glial cultures were found to have a high (Kd approximately equal to 10 nM) as well as a low (Kd approximately equal to 240 nM) affinity binding site. Glial cultures also had a similarly high affinity site (Kd 13 nM). In both types of cultures, the high affinity site was Ro 5-4864 sensitive and clonazepam resistant. Since Ro 5-4864 has particular affinity for non-neuronal elements and clonazepam for neuronal elements, the data suggest that the high affinity binding site may be localized to glial elements and the low affinity site primarily neuronal.

Benzodiazepines and beta-adrenergic binding to primary cultures of astrocytes and neurons

Characteristics of primary cultures of neurons or of astrocytes are discussed which suggest that such cultures are appropriate models for their in vivo counterparts. Advantages or disadvantages of these cultures for studies of receptor binding are: Neuronal and astrocytic binding can be studied separately. Binding can be studied to intact cells or after homogenization. Apparent binding to intact cells may include unspecific retention. This seems to be a problem for beta-adrenergic ligands but not for benzodiazepines.

Development of GABAergic function of dissociated hippocampal cultures from fetal mice

The GABA uptake mechanism has been characterized in hippocampal cell cultures prepared from fetal mice of 13-19 days gestational age [3H]GABA is accumulated selectively by neuronal cells by a high-affinity (Km = 3 micro M) mechanism that is an early property of the neurons. Autoradiography of [3H]GABA uptake revealed that approximately 30% of the neuronal cells had uptake. A unique small neuronal type did not have [3H]GABA uptake but was found to have [3H]glutamic acid uptake, suggesting that these neurons may be granule cells. The selective labeling of neurons with [3H]GABA and [3H]glutamic acid is consistent with the idea that high-affinity uptake of a transmitter may be unique to neurons that use that transmitter.