Abstract
1. Partially purified brain membranes obtained from male rough-skinned newts (Taricha granulosa) were used to determine the effects of Nad and temperature on the specific binding of the opioid receptor antagonist [3H]naloxone. 2. The addition of NaCl to the incubation medium at concentrations up to 400 mM produced a dose-related increase of the specific binding of [3H]naloxone. 3. The addition of other salts to the incubation medium had less pronounced effects: KC1 and MgCl2 slightly increased and decreased, respectively, the specific binding of naloxone, and CaCl2 had no effect. 4. Results of an equilibrium saturation experiment showed that the addition of 200 mM NaCl resulted in over a 10-fold increase in the number of high affinity (KD = 0.61 nM) binding sites for naloxone, with no changes in the number of low affinity (KD = 21.8 nM) binding sites. 5. Changes in NaCl concentrations did not significantly affect either dissociation constant. 6. The binding of [3H]naloxone was temperature-dependent; it increased when the incubation temperatures were elevated from 0°C to 37°C. 7. Results obtained for this urodele amphibian are compared with those available for other vertebrate species.