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(Circulation Research. 2008;102:86.)
© 2008 American Heart Association, Inc.

Cellular Biology

Electrostatic Contributions of Aromatic Residues in the Local Anesthetic Receptor of Voltage-Gated Sodium Channels

Christopher A. Ahern, Amy L. Eastwood, Dennis A. Dougherty, Richard Horn

From the Department of Molecular Physiology & Biophysics (C.A.A., R.H.), Institute of Hyperexcitability, Jefferson Medical College, Philadelphia, Pa; and Division of Chemistry and Chemical Engineering (A.L.E., D.A.D.), California Institute of Technology, Pasadena.

Correspondence to Dr Christopher Ahern, Departments of Anesthesiology, Pharmacology and Therapuetics, and Cellular and Physiological Sciences, University of British Columbia, 2176 Health Sciences Mall, Vancouver, British Columbia, Canada V6T IZ3. E-mail Christopher.Ahern{at}UBC.ca

Antiarrhythmics, anticonvulsants, and local anesthetics target voltage-gated sodium channels, decreasing excitability of nerve and muscle cells. Channel inhibition by members of this family of cationic, hydrophobic drugs relies on the presence of highly conserved aromatic residues in the pore-lining S6 segment of the fourth homologous domain of the channel. We tested whether channel inhibition was facilitated by an electrostatic attraction between lidocaine and electrons of the aromatic rings of these residues, namely a cation- interaction. To this end, we used the in vivo nonsense suppression method to incorporate a series of unnatural phenylalanine derivatives designed to systematically reduce the negative electrostatic potential on the face of the aromatic ring. In contrast to standard point mutations at the same sites, these subtly altered amino acids preserve the wild-type voltage dependence of channel activation and inactivation. Although these phenylalanine derivatives have no effect on low-affinity tonic inhibition by lidocaine or its permanently charged derivative QX-314 at any of the substituted sites, high-affinity use-dependent inhibition displays substantial cation- energetics for 1 residue only: Phe1579 in rNa_V1.4. Replacement of the aromatic ring of Phe1579 by cyclohexane, for example, strongly reduces use-dependent inhibition and speeds recovery of lidocaine-engaged channels. Channel block by the neutral local anesthetic benzocaine is unaffected by the distribution of electrons at Phe1579, indicating that our aromatic manipulations expose electrostatic contributions to channel inhibition. These results fine tune our understanding of local anesthetic inhibition of voltage-gated sodium channels and will help the design of safer and more salutary therapeutic agents.

Key Words: voltage-gated sodium channels • unnatural amino acids • local anesthetics • cardiac arrhythmias

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