Table 2

Inhibition constant (Ki) for select barbiturates andR(+)- or S(−)-enantiomers determined for inhibition of either binding or photolabeling of NCAs to their respective sites on nAChRs in the resting conformational state

BarbiturateKi
[14C]Amobarbital[3H]Tetracaine[125I]TID
μM
Amylbarbital2.6  ± 0.26.3  ± 1.03.3  ± 0.2
Amobarbital4.0  ± 0.38.5  ± 0.46.9  ± 0.4
Pentobarbital
 Racemic38  ± 4113  ± 5129  ± 8
R(+)113  ± 5
S(−)201  ± 12
Isobarbital
 Racemic54  ± 8152  ± 12144  ± 7
R(+)110  ± 24
S(−)209  ± 25

The Ki values (averaged) were calculated using the Cheng-Prusoff relationship (eq. 2) and the IC50 values obtained from Figs. 3 ([14C]amobarbital), 4A and 5 ([125I]TID), and 4B ([3H]tetracaine).