This study aims to address the question of the molecular mechanism for the inhibition of ionic conduction through voltage-dependent and neurotransmitter regulated channels by local anesthetics (LA). Specifically, we aim to probe the nature and the site of the blocking action of LA on voltage-dependent sodium channels and nicotinic cholinergic receptors. Our approach is to characterize the action of a series of LA on be single channel properties of synthetic channel peptides in lipid bilayers. The synthetic channel peptides are designed to mimic the channel lining of the mammalian brain voltage-dependent sodium channel with amino acid sequence -- DPWNWLDFTVITFAYVTEFVDL-- and of the nicotinic cholinetic receptor from fish electric organ with the sequence: EKMSTAISVLLAQAVFLLLTSQR. A series of LA well characterized on voltage-gated sodium channels and end-plate channels will be determined. The effect of LA on channel conductance, ionic selec- tivity and saturation will be evaluated. The modification of channel gating kinetics in terms of the number of channel open and closed states or the lifetime of the channel on each of these states will be assessed. The accessibility of the 2 aqueous compartments separated by the bilayer will allows to examine the pH-dependent action of these drugs under symmetric and asymmetric conditions. The concentration dependence, voltage dependence, temperature and calcium dependence of the channel block will be explored. The stereopotency ratio for block will be examined. The results will be compared with data on authentic channels. A salient advantage of this approach is that, by chemical synthesis, an amino acid thought to be crucial for the action of LA can be substituted. The assay of the """"""""analogue"""""""" will establish if such residue is significant. Cases in point are the analogues of the sodium channel peptide in which the acidic residues D7 or E18 (located in the pore lumen), D1 (pore entry) or D21 (pore exit) are substituted or the uncharged amino acids N or Q, respectively. Likewise, for the receptor peptide, the channel activity of analogues in which the polar residues S8 and T5 (located in the pore lumen) are replaced for L and El or K2 (pore entry) are substituted for Q and A, respectively, will be analyzed. This program may lead to identify the molecular structures that determine the pharmacological specificity in the action of LA on channel proteins and will provide information conducive to formulate a common mechanism for the inhibitory action of the clinically important local anesthetics on voltage-dependent channels in neural and cardiac cells.
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