PT - JOURNAL ARTICLE AU - Annamaria De Luca AU - Sophie Talon AU - Michela De Bellis AU - Jean-François Desaphy AU - Giovanni Lentini AU - Filomena Corbo AU - Antonio Scilimati AU - Carlo Franchini AU - Vincenzo Tortorella AU - Diana Conte Camerino TI - Optimal Requirements for High Affinity and Use-Dependent Block of Skeletal Muscle Sodium Channel by <em>N</em>-Benzyl Analogs of Tocainide-Like Compounds AID - 10.1124/mol.64.4.932 DP - 2003 Oct 01 TA - Molecular Pharmacology PG - 932--945 VI - 64 IP - 4 4099 - http://molpharm.aspetjournals.org/content/64/4/932.short 4100 - http://molpharm.aspetjournals.org/content/64/4/932.full SO - Mol Pharmacol2003 Oct 01; 64 AB - Newly synthesized tocainide analogs were tested for their state-dependent affinity and use-dependent behavior on sodium currents (INa) of adult skeletal muscle fibers by means of the Vaseline-gap voltage clamp method. The drugs had the pharmacophore amino group constrained in position α [N-(2,6-dimethylphenyl)pyrrolidine-2-carboxamide (To5)] or β [N-(2,6-dimethylphenyl)pyrrolidine-3-carboxamide (To9)] in a proline-like cycle and/or linked to a lipophilic benzyl moiety as in N-benzyl-tocainide (Benzyl-Toc), 1-benzyl-To5 (Benzyl-To5), and 1-benzyl-To9 (Benzyl-To9). INa were elicited with pulses to -20 mV from different holding potentials (-140, -100, and -70 mV) and stimulation frequencies (2 and 10 Hz). All compounds were voltage-dependent and use-dependent channel blockers. The presence of a proline-like cycle increased the potency; i.e., To5 was 3- and 10-fold more effective than Toc in blocking INa at the holding potential of -140 and -70 mV, respectively. The benzyl group on the amine further enhanced drug effectiveness with the following scale: Benzyl-To9 ≥ Benzyl-Toc &gt; Benzyl-To5. At a holding potential of -100 mV and 10-Hz stimulation, Benzyl-To9 blocked INa with a half-maximal concentration of 0.5 μM, being 60 and 400 times more potent than To9 and Toc, respectively. The similar effectiveness of Benzyl-Toc and Benzyl-To9 was paralleled by a similar spatial arrangement by equilibrium geometry modeling. In addition, the latter had a higher pKa value that probably contributed to a slow kinetic during its high use-dependent behavior. Benzyl-To5 had its lowest energy level at a more folded conformation that justifies the less favorable profile among the N-benzylated analogs. The new compounds are the most potent tocainide-like sodium channel blockers so far described and have high therapeutic potentials.