Interactions between Local Anesthetics and Na⁺ Channel Inactivation Gate Peptides in Phosphatidylserine Suspensions as Studied by ¹H-NMR Spectroscopy

Abstract

Interactions between local anesthetics and a sodium channel inactivation gate peptide (Ac-GGQDIFMTEEQK-NH₂, MP-1A), which was dissected from the cytoplasmic linker between domains III and IV of the sodium channel α-subunit (G1484-K1495 in rat brain type IIA), have been studied by ¹H-NMR spectroscopy. Changes in ¹H-NMR chemical shifts of the aromatic proton resonances of dibucaine (pH 7.0) and lidocaine (pH 6.0 and 9.0) in phosphatidylserine (PS) suspensions were observed. The effects of substitution of glutamine (F1489Q; MP-2A) or D-phenylalanine (MP-1A') for L-phenylalanine (F1489) in MP-1A and the effects of substitution of neutral amino acid residues for the corresponding acidic amino acid residues (D1487N, MP-1NA; E1492Q, MP-1QEA; E1493Q, MP-1EQA) in MP-1A, on the aromatic ¹H-NMR cheimcal shift changes of dibucaine and lidocaine were also investigated. From these results it was concluded that : the aromatic ring of phenylalanine of MP-1A and the aromatic ring of the cationic form of dibucaine or lidcaine are interacting by π-π stacking; the tertiary amine nitrogen of dibucaine is interacting electrostatically with D1487, whereas that of lidocaine is interacting with E1492.