TY - JOUR
T1 - Activation and block of mouse muscle-type nicotinic receptors by tetraethylammonium
AU - Akk, Gustav
AU - Steinbach, Joe Henry
PY - 2003/8/15
Y1 - 2003/8/15
N2 - We have studied the activation and inhibition of the mouse muscle adult-type nicotinic acetylcholine receptor by tetraethylammonium (TEA) and related quaternary ammonium derivatives. The data show that TEA is a weak agonist of the nicotinic receptor. No single-channel clusters were observed at concentrations as high as 5 mM TEA or in the presence of a mutation which selectively increases the efficacy of the receptor. When coapplied with 1 mM carbamylcholine (CCh), TEA decreased the effective opening rate demonstrating that it acts as a competitive antagonist of CCh-mediated activation. Kinetic analysis of currents elicited by CCh and TEA allowed an estimate of receptor affinity for TEA of about 1 mM, while an upper limit of 10 s-1 could be set for the wild-type channel-opening rate constant for receptors activated by TEA alone. At millimolar concentrations, TEA inhibited nicotinic receptor currents by depressing the single-channel amplitude. The effect had an IC50 of 2-3 mM, depending on the conditions of the experiment, and resembled a standard open-channel block. However, the decrease in channel amplitudes was not accompanied by an increase in the mean burst duration, indicating that a linear open-channel blocking mechanism is not applicable. Upon studying block by other nicotinic receptor ligands it was found that block by CCh, tetramethylammonium and phenyltrimethyl-ammonium can be accounted for by the sequential blocking mechanism while block in the presence of methyltriethylammonium, ethyltrimethylammonium or choline was inconsistent with such a mechanism. A mechanism in which receptors blocked by TEA can close would account for the experimental findings.
AB - We have studied the activation and inhibition of the mouse muscle adult-type nicotinic acetylcholine receptor by tetraethylammonium (TEA) and related quaternary ammonium derivatives. The data show that TEA is a weak agonist of the nicotinic receptor. No single-channel clusters were observed at concentrations as high as 5 mM TEA or in the presence of a mutation which selectively increases the efficacy of the receptor. When coapplied with 1 mM carbamylcholine (CCh), TEA decreased the effective opening rate demonstrating that it acts as a competitive antagonist of CCh-mediated activation. Kinetic analysis of currents elicited by CCh and TEA allowed an estimate of receptor affinity for TEA of about 1 mM, while an upper limit of 10 s-1 could be set for the wild-type channel-opening rate constant for receptors activated by TEA alone. At millimolar concentrations, TEA inhibited nicotinic receptor currents by depressing the single-channel amplitude. The effect had an IC50 of 2-3 mM, depending on the conditions of the experiment, and resembled a standard open-channel block. However, the decrease in channel amplitudes was not accompanied by an increase in the mean burst duration, indicating that a linear open-channel blocking mechanism is not applicable. Upon studying block by other nicotinic receptor ligands it was found that block by CCh, tetramethylammonium and phenyltrimethyl-ammonium can be accounted for by the sequential blocking mechanism while block in the presence of methyltriethylammonium, ethyltrimethylammonium or choline was inconsistent with such a mechanism. A mechanism in which receptors blocked by TEA can close would account for the experimental findings.
UR - http://www.scopus.com/inward/record.url?scp=0041353447&partnerID=8YFLogxK
U2 - 10.1113/jphysiol.2003.043885
DO - 10.1113/jphysiol.2003.043885
M3 - Review article
C2 - 12824448
AN - SCOPUS:0041353447
SN - 0022-3751
VL - 551
SP - 155
EP - 168
JO - Journal of Physiology
JF - Journal of Physiology
IS - 1
ER -