No abstract

In order to test the suggestion that antipsychotic drugs act by blocking dopamine receptors in the brain, the direct effects of such neuroleptic drugs were tested on the stereospecific binding of [3Hldopamine and of [3H]haloperidol to rat brain striata and their subfractions.

SE~RZAN, P., CLIAIJ-WOM;, M., and MOYYFN, S. 8972. The r-nicnabranc binding of morphine, diphenylhydantoin, and teirahydrocannabi~aol. Can. J . Physiol. Pharrnasol. 50, 1193-1200.The adsorption of rnorgshirae to guinea pig brain synaptosornc membranes and to human erythrocyte rncmbranes was found lo be passive, and unaffectec8 by time, tanperature, o~aabain, dinitrophenol, saponin, or ATP. ' Y' he mernbrane/buffer partition coefficient for niorphine was 35 (at low ionic strength) and i . 2 (at high ionic strength). The synaptosome membrane/buffer partition coefficient for diphenylk~ydaralclin was around 60 (at pH 8), while that for A()-tetrahydrocannabinol (THC) was around 380 (in the concentration range of around 10-"M). The partition cc>efficient for the latter dsug dropped by a factor of two G;. three with increasing drug col-mcentrations for both erythrocyte ghosts and synaptosomes; there may be two types of binding sitcs for THC. The minimu111Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by University of Auckland on 12/07/14For personal use only.Fnc;. 4. A double reciprocal plot of thc data of Fig. 3 indicates that the points fall on a single line, suggesting that there is one set of binding sites h r diphenylhydantoin (at p H 10.5).Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by University of Auckland on 12/07/14For personal use only.

ABSTRACIIn order to develop a better dopamine receptor The homogenates from the human brain regions were prepared in the same way as those from the calf caudate, except that the preliminary crude homogenates of human brain were frozen in 1-ml aliquots, and after centrifugation they were resuspended in only 3 ml of buffer. Thus, the protein concentrations of both the human and calf homogenates were kept approximately equal. Optimum homogenization with the Polytron was obtained at a setting of 6 (for 20 sec) using a 16 X 100 mm glass test tube to hold the small 3-ml volume. Polytron settings greater than 6 (for 3 ml) caused a loss in binding sites; for calf homogenates, the optimum occurred at 7 (for 10 ml). (220), an aliquot of 0.5 ml was removed (polypropylene pipette tip) from the mixture and filtered under reduced pressure through a glass fiber filter (GF/B, Whatman, 24 mm diameter) using a Millipore stainless steel mesh support for the filter; the filtration took less than 1 sec. The filter was then washed twice with 5 ml of buffer per wash. The buffer was used at room temperature since minor differences in binding were found with the buffer at 40 or 37°. The wash buffer was delivered by gravity from a syringe Re-pipette over a period of 4 sec. The filters were not blotted or dried but placed directly into liquid scintillation vials; 8 ml of Aquasol (New England Nuclear Corp.) were added and the samples were monitored for 3H (25) after they were stored at 40 for at least 6 hr to allow temperature equilibration and to permit the glass fiber filters to become uniformly translucent. Specific binding of apomorphine was defined as that amount bound in the presence of 1 MM (-)-butaclamol minus that bound in the presence of 1 AM (+)-butaclamol, in accordance with previous work (7, 9) on dopamine receptors. The results were calculated in terms of femtomoles of apomorphine specifically bound per mg of homogenate protein. Apomorphine is sufficiently hydrophobic and surface-active to warrant measuring the unbound (free) concentration (26)(27)(28)

This study shows that Ca2+ reversed the nerve-blocking actions of procaine, lidocaine, procainamide, imipramine, chlorpromazine, tetrodotoxin, hexanol, heptanol, benzyl alcohol, thymol, sodium barbital, and sodium pentobarbital. Using the rat phrenic nerve, it was found that an elevation of external Ca2+ (from 0.22 mM to 4.4 mM) restored the blocked compound action potential of the nerve by around 30% for all three types of drugs: cationic, anionic, and uncharged.The high Ca2+ level of 4.4 mM displaced chlorpromazine from brain synaptosome membranes, but did not displace heptanol, pentobarbital, or lidocaine. Since there was no relation between blockade reversal and drug displacement by Ca2+, the data do not support the idea that Ca2+ and drugs compete for membrane-binding sites. Since approximately the same magnitude of reversal occurred with different drugs, as well as with tetrodotoxin, it is concluded that Ca2+ may cause a physiological kind of allosteric antagonism of the drug-blocked Na+ channel, or a direct augmentation of the Na+ conductance.