Conformational states of the nicotinic acetylcholine receptor from Torpedo californica induced by the binding of agonists, antagonists, and local anesthetics. Equilibrium measurements using tritium-hydrogen exchange

Abstract

The tritium-hydrogen exchange kinetics of Torpedo californica AChR, in native membrane vesicles at pH 7.4 and 0 degrees C, have been analyzed in the presence of agonists, partial agonists, local anesthetics, and competitive antagonists. The agonists carbamylcholine (10 microM-1 mM) and suberyldicholine (10 microM) and the partial agonists decamethonium (25 microM and 1 mM) and hexamethonium (1 mM) have no effect on the exchange kinetics, although at lower concentration carbamylcholine may slightly accelerate exchange. Nondesensitizing local anesthetics do affect the exchange behavior, dependent on concentration. Procaine at 500 microM moderately retards exchange while procaine at 10 mM and tetracaine at 5 mM slightly accelerate exchange. The competitive antagonist alpha-bungarotoxin retards exchange significantly, as does d-tubocurarine although to a lesser extent. These results suggest that the resting and desensitized conformations of the AChR are very similar in overall solvent accessibility and that at lower concentrations noncompetitive blockers such as procaine may stabilize a less solvent-accessible state of the AChR. The competitive antagonists alpha-bungarotoxin and d-tubocurare also stabilize a dynamically restricted, less solvent-accessible conformation of the acetylcholine receptor, demonstrating that a large conformational change accompanies binding of these toxins. Any change in conformation which may accompany desensitization is very different from these effects.

Photoactivatable α‐conotoxins reveal contacts with all subunits as well as antagonist‐induced rearrangements in the Torpedo californica acetylcholine receptor

“…It has been demonstrated previously [53] that the rate of tritium–hydrogen exchange in the membrane‐bound AChR was considerably decreased in the presence of αBgt. This effect was explained by αBgt stabilization of a more rigid and less solvent‐accessible conformation of the receptor.…”

Local anesthetics inhibit receptors coupled to phosphoinositide signaling in

“…In addition to their actions on voltage-activated ion channels, LA are also known to block some ligandactivated ion currents, including those activated by both types of mammalian acetylcholine (ACh) receptors [2], the Torpedo electric organ nicotinic receptor [3], and the mammalian ryanodine receptor in skeletal muscle [4]. Currents through second-messenger-activated ion channels coupled to heterotrimeric G-protein-linked receptors can also be inhibited by LA, as was demonstrated for the muscarinic ACh receptor [5].…”

Incorporation of the nicotinic acetylcholine receptor into planar multilamellar films: characterization by fluorescence and Fourier transform infrared difference spectroscopy

“…It has been studied by a variety of biophysical, biochemical, and electrophysiological techniques and is the best characterized neurotransmitter receptor/ion channel in terms of both structure and function. Unfortunately, due to the relatively low atomic resolution structural information available for the nAChR (Brisson and Unwin, 1985;Mitra et al, 1989), details of the structural differences between the resting, open, and desensitized states (Unwin et al, 1988;McCarthy and Stroud, 1989;Mielke and Wallace, 1988) and information about the mechanism by which the binding of acetylcholine leads to channel gating and desensitization are limited.…”