Key words: Sodium channels — Local anesthetics — Benzocaine — Butamben — Phospholipid membranes —2H NMR
Springer Online Journal Archives 1860-2000
Chemistry and Pharmacology
Abstract. This paper presents experimental evidence that an aromatic compound that has a quadrupole moment locates in a polar headgroup region in the lipid membranes, but not in a membrane interior hydrophobic region, and discusses correlation to the site of action of benzocaine and butamben on sodium channels. The 2H NMR spectra of benzocaine-d4, benzocaine-d5, butamben-d4, and butamben-d9 in the model membranes were observed. The 2H NMR spectra of perdeuterated palmitic acid and selectively deuterated palmitic acids at C2, C3, C5, C6, C9, or C10, which were inserted into the lipid membranes, were also observed. The phosphatidylserine (PS), phosphatidylcholine (PC), and liquid mixtures composed of PS, PC, and phosphatidylethanolamine (PE), which contain or do not contain cholesterol, were employed. A moment analysis was applied to the 2H NMR spectra of palmitic-d31 acid. An order parameter, S CD , for each carbon segment was calculated from the observed quadruple splitting. We concluded that in the lipid mixture containing cholesterol, the aromatic rings of benzocaine and butamben locate around the glycerol moiety of the lipids and that when there exists no cholesterol, they locate a little more inside from the headgroup region, directing, in both cases, their amino groups upward (polar region) and the ethyl and butyl groups downward (hydrophobic region). These data cast a question on the site of action of the neutral local anesthetics in the sodium channels.
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