The effect of pertussis toxin on dopamine and haloperidol competition of [3H]raclopride binding to D3 (A) and D2A(B) receptors
| Untreated | PTX Treated | ||||
|---|---|---|---|---|---|
| − Na | + Na | − Na | + Na | ||
| D3receptors | Affinity (nM) | Affinity (nM) | |||
| Dopamine | 4.92 ± 1.96 | 16.2 ± 2.7 | 4.02 ± 0.59 | 24.4 ± 2.2 | |
| Khigh | 0.50 ± 0.23 | 0.45 ± 0.16 | |||
| Klow | 15.3 ± 2.9 | 28.7 ± 1.2 | |||
| Rhigh | 53 ± 5% | 24 ± 5% | |||
| Haloperidol | 0.74 ± 0.12 | 1.77 ± 0.07 | 0.54 ± 0.20 | 2.21 ± 0.26 | |
| D2Areceptors | |||||
| Dopamine | 177 ± 55 | 759 ± 44-a | 863 ± 19 | 2510 ± 300 | |
| Khigh | 1.96 ± 0.89 | ||||
| Klow | 379 ± 7 | ||||
| Rhigh | 29 ± 5% | ||||
| Haloperidol | 0.12 ± 0.02 | 0.44 ± 0.01 | 0.09 ± 0.04 | 0.36 ± 0.06 | |
The competition studies were performed and the inhibition constants were calculated as described in “Methods.”
The results are means ± S.E.s of two to four experiments. −Na and +Na; the buffer contained 120 mM NMDG and 120 mM NaCl, respectively. Khigh and Klow represent the affinity values of high and low affinity binding sites, respectively, and are given when the data were best described with a two-site analysis. Rhigh indicates the percentage of receptors in the high affinity state. PTX; pertussis toxin.
↵4-a Value analyzed by a one-site model, although a significantly better fit was achieved with a two-site model. A too low proportion of the high affinity agonist sites was present in the presence of sodium for reliable Khigh and Klow values.