TABLE 3

Reconstructions of K_{p brain} ratios (P-glycoprotein function at the blood-brain barrier) and K_{p brain} values of P-glycoprotein substrate verapamil in control, pentylenetetrazole, phenytoin, and spontaneous model of epilepsy mice

Reconstructed brain-to-plasma concentration ratios (K_{p brain}) were calculated from the reported in vitro P-glycoprotein (P-gp) efflux ratio of verapamil (Uchida et al., 2011a), the reported protein expression level of P-gp/mdr1a in P-gp/mdr1a–expressing LLC-PK1 cell monolayer (Uchida et al., 2011a), and the protein expression level of P-gp/mdr1a in brain capillaries isolated from control, PTZ, EL, and PHT mice, using eq. 2 described in Materials and Methods. Unbound fractions of verapamil in plasma (f_u,plasma) and brain (f_u,brain) were determined by the equilibrium dialysis method and brain slice uptake method, respectively. Plasma was spiked with 500 nM verapamil and dialyzed against phosphate-buffered saline buffer (pH 7.4) at 37°C for 6 hours (n = 3–4). Brain slices (500 μm) were incubated in extracellular fluid buffer (pH 7.4) containing 50 nM verapamil at 37°C for 6 hours (n = 3–4). The reconstructed K_{p brain} values were calculated from the reconstructed K_{p brain} ratios and the f_u,plasma and f_u,brain values using eq. 3 described in Materials and Methods. Each value represents the mean ± S.E.M. The S.E.M. was calculated according to the law of propagation of error.