Table 2

Properties of the [3H] ifenprodil binding sites in guinea pig brain and liver

LiverBrain
IC50SlopeIC50Slope
nm nm
Ifenprodil2.4  ± 0.70.95  ± 0.151.7  ± 0.40.85  ± 0.05
Haloperidol6.8  ± 2.80.64  ± 0.082-a 23  ± 60.64  ± 0.042-a
Ditolylguanidine122  ± 330.55  ± 0.052-b 36  ± 110.70  ± 0.092-b
Trifluoperazine11  ± 21.10  ± 0.1313  ± 10.93  ± 0.06
(−) -Emopamil28  ± 151.00  ± 0.1234  ± 170.81  ± 0.09

Microsomes from guinea pig liver and brain were prepared as described in Experimental Procedures. Saturation analysis revealedB max values of the liver and brain [3H] ifenprodil binding sites of 42 ± 3 and 7.6 ± 0.2 pmol/mg of microsomal protein (n = 3) (K d = 2.5 ± 0.8 and 1.9 ± 0.6 nm, respectively; (n = 3).

    • Data shown are mean ± standard deviation (n = 3).

    • Biphasic fitting of the data (see Fig. 2) gave the following IC50 values.

    • ↵2-a Haloperidol: Liver IC50 (high) = 2.9 ± 1.6 nm, IC50 (low) = 141 ± 67 nm(30 ± 6% of sites); brain IC50 (high) = 11 ± 8 nm, IC50 (low) = 1,720 ± 1,060 nm(16 ± 2% of sites).

    • ↵2-b Ditolylguanidine: Liver IC50 (high) = 22 ± 8 nm, IC50 (low) = 4,500 ± 1,400 nm(34 ± 6% of sites); brain IC50 (high) = 27 ± 4 nm, IC50 (low) = 24,000 ± 8,000 nm (12 ± 2% of sites).