enkephalinamide-leu--ala(2)- and Glioma

Binding activity of the enkephalin dimer [D-Ala2, Leu5-NH-CH2-]2 (DPE2) to NG108-15 hybrid cells was compared to that of the monomer [D-Ala2, Leu5]enkephalin amide (DALEA). At 25 degrees C, the values of the apparent affinity constant for DPE2, measured to intact and lysed cells and membranes, was 5.0 (+/- 0.09) X 10(9) M-1 for n = 28 experiments, as compared to 0.9 (+/- 0.08) X 10(9) M-1 (n = 16) for DALEA. At 4 degrees C, the binding affinity of DPE2 decreased by 43% and that of DALEA by 33%. An important difference between the binding of DPE2 and DALEA was that, after necessary corrections for difference in maximal "bindability" of the respective tritiated enkephalins, the molar binding capacity for DALEA was twofold higher than for DPE2, although mutual cross-displacement studies indicated that binding occurred to one class of noninteracting homogeneous receptors. The binding capacity for intact and lysed cells and membranes was 20 (+/- 2) X 10(-11) M for DPE2 and 43 (+/- 2) X 10(-11) M for DALEA. The enkephalin monomers [D-Ala2, D-Leu5]enkephalin (DADLE) and [D-Ala2, Met5]enkephalin amide (DAMEA) showed binding characteristics similar to those of DALEA.

Topics: Animals; Cell Line; Cell Membrane; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalin, Methionine; Glioma; Neuroblastoma; Receptors, Opioid; Tritium

The equilibrium binding and dissociation kinetics of the enkephalin dimer bis-(D-Ala2-D-Leu5-enkephalin)-ethylenediamide (designated DPE2) to neuroblastoma glioma NG108-15 cells were investigated and compared with the monomers D-Ala2-D-Leu5-enkephalin (DADL) and D-Ala2-Leu5-enkephalinamide (DALEA). Binding was studied after exposure of the membrane to increasing concentrations of the irreversible delta receptor selective ligand FIT in order to decrease the density of binding sites on the cell membrane. The increased affinity of DPE2 did not revert to that of the monomer DADL by this reduction of binding sites. Similarly, the dissociation of DPE2 did not approach that of the monomer DALEA in the presence of 1 microM DALEA. These data strongly suggest that crosslinking does not occur, and fail to confirm the hypothesis that dimers with short spanning chain length aid the clustering of receptors. We postulate: 1) If the dimer binds to a bivalent binding site, the monovalent binding state of our bivalent ligand may not exist to an appreciable extent, and 2) the bivalent ligand cannot bind when the binding site is irreversibly blocked by a monovalent ligand.

Topics: Animals; Cell Line; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Glioma; Kinetics; Models, Neurological; Neuroblastoma; Receptors, Opioid; Receptors, Opioid, delta

Opiate receptor down-regulation in neuroblastoma X glioma NG108-15 hybrid cells possibly involved the internalization of ligand-receptor complexes during chronic treatment. However, receptor internalization was not supported by the observed decrease in [3H] enkephalin(D-Ala2,D-Leu5) ( [3H]DADLE) associated with the hybrid cells during prolonged incubation with 10 nM [3H]DADLE at 37 degrees C. This decrease in [3H]DADLE bound was determined to be due to degradation of the ligand-receptor complexes, for a time-dependent increase in [3H]DADLE bound was observed when the incubations were carried out in the presence of 0.1 mM chloroquine. The increase did not exceed the amount of down-regulated receptor, could be blocked by naloxone, and was not observed at 24 degrees C. The [3H]DADLE bound in the presence of chloroquine was not sensitive to trypsin or to 20 microM diprenorphine. The accumulated [3H]DADLE was demonstrated to be intracellularly located by the fractionation of the homogenates in self-generating Percoll gradients. In the presence of chloroquine, a time-dependent translocation of [3H]DADLE from the plasma membrane-enriched fractions to the lysosome-enriched fractions was observed. The translocation was not observed at 24 degrees C in the presence of chloroquine or at 37 degrees C in the absence of chloroquine. The [3H]DADLE in the lysosome-enriched fractions was not sensitive to trypsin and remained bound in the presence of chloroquine. With the removal of chloroquine, an increase in the release of [3H]DADLE into the medium was observed. Sephadex G-50 column chromatography of the sodium deoxycholate extracts of the lysosome-enriched fractions suggested that the [3H]DADLE was bound to macromolecules intracellularly. Thus, chronic [3H]DADLE treatment of the hybrid cells resulted in an internalization of ligand-receptor complexes which were degraded in the lysosomes. Subsequently, the [3H]DADLE was regurgitated by the hybrid cells.

Topics: Animals; Cell Line; Chloroquine; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Glioma; Hybrid Cells; Kinetics; Lysosomes; Mice; Neuroblastoma; Rats; Receptors, Opioid