Faculty Bibliography

Cocaine and its analogs bound saturably to membranes of brain and liver of mice. The binding sites on membranes of liver had a lower affinity for cocaine than those of brain. In addition, there were striking differences between the two tissues in regard to the relative potencies of cocaine analogs in competing with [3H]cocaine for binding. In comparison with the binding sites in brain, those in liver had only moderate stereospecificity, and they discriminated less between the centrally active compounds and the centrally inert analogs

Various opiate ligands were bound to brain membranes of mice of the Recombinant Inbred System. The specific binding of low levels of [3H]naloxone, [3H]dihydromorphine and [3H]ethylketocyclazocine was disturbed in a similar fashion among the inbred strains, and in a pattern different from that observed for [3H](D-Ala2,D-Leu5)-enkephalin. The results indicate that the inbred strains differ in mu- and delta-type binding and support the concept of multiple opiate receptors in mouse brain

Kinetic experiments indicate that association of [3H]-cocaine to its binding site in brain occurs rapidly (seconds). Dissociation of membrane-bound cocaine is also rapid, with a dissociation half-life in seconds; this raises the question of whether membrane-bound cocaine is released during the time required for rapid filtration of tissue-containing filters. Results from experiments with increasing numbers of filter-washes indicate that there is no significant loss of [3H]-cocaine saturably bound to brain membranes within the time-scale of the rapid filtration procedure. In addition, saturation analysis of binding data obtained with the filtration procedure and with the centrifugation method give similar estimates of the affinity (dissociation constant: 0.8 microM) and the maximal binding (5 pmol/mg of protein) of cocaine. However, the nonspecific binding and the experimental error in the saturable binding are considerably greater in centrifugation assays than in filtration assays

(+/-)-[3H]Nicotine was bound saturably to crude particulate, and synaptosomal-mitochondrial fraction from mouse brain. Scatchard and Hill plots of the binding data are in agreement with the existence of two independent classes of binding sites with high (Kd of 0.1-0.4 microM) and low(Kd is 20 microM) affinities, although negative cooperativity or a two-step model of ligand-receptor interaction cannot be ruled out. Nicotinic or muscarinic agonists and antagonists had little or no affinity for the nicotine binding sites, suggesting that nicotine binds in brain to noncholinergic sites. The binding did not display stereospecificity; this is consistent with the similarity in the pharmacological effects of (-)- and (+)-nicotine. Our results indicate that binding studies with [3H]nicotine should be interpreted with extreme caution

The supernatant fraction of centrifuged homogenate of brain tissue contains material that inhibits the saturable binding of [3H]cocaine to crude mouse brain membranes. This material was subjected to heat treatment to remove protein; further purification was achieved by filtering through an Amicon UM-10 membrane ultrafilter and gel filtration of the ultrafiltrate on Sephadex G-25. Sensitivity to acid hydrolysis and peptidase action indicates that the inhibitory activity resides in peptide material with low molecular weight. The partially purified inhibitor has similar effects to that of cocaine on the specific binding of various ligands to opiate and nonopiate receptors in mouse brain membranes