1. A pair of
benzamide analogues containing a pyrrolidinyl or piperidinyl group was examined for their
anticonvulsant activity against the electroshock-induced
seizures in mice and the ability to block the voltage-gated Na channel in N1E-115 cells, in comparison with the prototype compound,
U-54494A, (+/-)-cis-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]-ben zam ide , a potent
anticonvulsant and a Na channel blocker. 2. The pyrrolidinyl
benzamide (U-49524E) was found to be effective against the electroshock-induced
seizures (ED50 = 35 mg kg-1, i.p.) whereas the
benzamide with a piperidinyl moiety (U-49132E) was inactive (ED50 greater than 100 mg kg-1). 3. Using whole-cell patch clamp techniques we found that
U-49132E was several times less potent, with an IC50 of 396 microM as compared to 118 microM for
U-49524E at the holding potential of -80 mV, and was much slower in blocking Na channels with a half-time of 10.7 +/- 1.1 min vs. 2.2 +/- 0.4 min for its counterpart. 4. Qualitatively, their general modes of interaction with Na channels were similar to each other and to that of
U-54494A in that they interacted with the resting and slowly-inactivated states of the channels and exhibited a use-dependent inhibition because of a slow recovery from the inactivated state in the presence of the drugs. 5. Comparison of their physicochemical properties, shows the less potent and slowly acting
U-49132E is more hydrophobic and bulkier than
U-49524E, but has the same pKa. This suggests that the drugs approach the Na channel through a narrow and hydrophilic pathway.6. Overall, this study underscores the importance of inhibiting the Na channel to the
anticonvulsant activity of the
benzamide compounds.