TABLE 2

Competition ligand binding analyses Competition binding studies were performed for the indicated competing ligands, versus [3H]nemonapride and [3H]spiperone, using different preparations of Sf9 cell membranes expressing the D2 dopamine receptor as in Table 1, in buffers with and without 100 mM sodium ions, as described under Materials and Methods. Data were fitted to one- and two-binding site models, and the parameters for the best fits are presented (Ki for a one-binding site model, and two Ki values (Kh, Kl) and the respective percentages of sites(%Rh, %Rl) for a two-binding site model). Parameters are expressed as mean ± S.E.M. from three or more experiments. Experiments with preparation 3 included 0.1% bovine serum albumin as described under Materials and Methods.

Ligands/Radioligands and Parameters Preparation 1 Preparation 3
Control Na+ Control Na+
Nemonapride/[3H]spiperone
   pKH or pKi (%Rh) 10.87 ± 0.08 (47 ± 6) 11.47 ± 0.18* 10.48 ± 0.09 (45 ± 5) 10.94 ± 0.04*
   pKL (%Rl) 8.22 ± 0.05 (53 ± 6) 7.84 ± 0.04 (55 ± 5)
Raclopride/[3H]spiperone
   pKH (%Rh) 8.93 ± 0.28 (28 ± 7)
   pKL or pKi (%Rl) 6.28 ± 0.15 7.95 ± 0.12* 6.22 ± 0.09 7.69 ± 0.14* (72 ± 7)
Spiperone/[3H]nemonapride
   pKH or pKi (%Rh) 11.33 ± 0.11 11.44 ± 0.12 (32 ± 3) 11.31 ± 0.20 10.91 ± 0.17 (48 ± 6)
   pKL (%Rl) 9.31 ± 0.10* (68 ± 3) 9.36 ± 0.09* (52 ± 6)
Raclopride/[3H]nemonapride
   pKi N.D. N.D. 6.61 ± 0.08 7.72 ± 0.07*
  • N.D., not determined

  • * P < 0.05 relative to control