TY - JOUR
T1 - Contrasting actions of philanthotoxin-343 and philanthotoxin-(12) on human muscle nicotinic acetylcholine receptors
AU - Brier, Tim J
AU - Mellor, Ian R
AU - Tikhonov, Denis B
AU - Neagoe, Ioana
AU - Shao, Zuoyi
AU - Brierley, Matt J
AU - Strømgaard, Kristian
AU - Jaroszewski, Jerzy W
AU - Krogsgaard-Larsen, Povl
AU - Usherwood, Peter N R
PY - 2003/10
Y1 - 2003/10
N2 - Whole-cell recordings and outside-out patch recordings from TE671 cells were made to investigate antagonism of human muscle nicotinic acetylcholine receptors (nAChR) by the philanthotoxins, PhTX-343 and PhTX-(12). When coapplied with acetylcholine (ACh), PhTX-343 caused activation-dependent, noncompetitive inhibition (IC50 = 17 microM at -100 mV) of whole-cell currents that was strongly voltage-dependent. However, preapplication of PhTX-343 unveiled a voltage-independent antagonism that also required receptor activation, which is suggestive of desensitization enhancement. In single-channel studies, 10 microM PhTX-343 significantly reduced the mean open time of channel openings evoked by 1 microM ACh from 4.42 +/- 0.44 to 1.58 +/- 0.10 ms with a minor increase (1.26-fold) in mean closed time. These data indicate that PhTX-343 predominantly blocks the open channel gated by ACh. In contrast, PhTX-(12) caused potent (IC50 = 0.77 microM at-100 mV), activation-dependent, noncompetitive inhibition of ACh-induced whole-cell currents that was only weakly voltage-dependent and suggestive of desensitization enhancement. It caused only a small decrease (7.5%) in the mean open time of channel openings induced by 1 microM ACh, whereas the mean closed time was significantly increased from 200 +/- 45 ms to 586 +/- 145 ms. The different voltage-dependencies of the two modes of action of these philanthotoxins suggest two binding sites, one deep in the nAChR pore, the other near the extracellular entrance to the pore.
AB - Whole-cell recordings and outside-out patch recordings from TE671 cells were made to investigate antagonism of human muscle nicotinic acetylcholine receptors (nAChR) by the philanthotoxins, PhTX-343 and PhTX-(12). When coapplied with acetylcholine (ACh), PhTX-343 caused activation-dependent, noncompetitive inhibition (IC50 = 17 microM at -100 mV) of whole-cell currents that was strongly voltage-dependent. However, preapplication of PhTX-343 unveiled a voltage-independent antagonism that also required receptor activation, which is suggestive of desensitization enhancement. In single-channel studies, 10 microM PhTX-343 significantly reduced the mean open time of channel openings evoked by 1 microM ACh from 4.42 +/- 0.44 to 1.58 +/- 0.10 ms with a minor increase (1.26-fold) in mean closed time. These data indicate that PhTX-343 predominantly blocks the open channel gated by ACh. In contrast, PhTX-(12) caused potent (IC50 = 0.77 microM at-100 mV), activation-dependent, noncompetitive inhibition of ACh-induced whole-cell currents that was only weakly voltage-dependent and suggestive of desensitization enhancement. It caused only a small decrease (7.5%) in the mean open time of channel openings induced by 1 microM ACh, whereas the mean closed time was significantly increased from 200 +/- 45 ms to 586 +/- 145 ms. The different voltage-dependencies of the two modes of action of these philanthotoxins suggest two binding sites, one deep in the nAChR pore, the other near the extracellular entrance to the pore.
KW - Cells, Cultured
KW - Humans
KW - Phenols
KW - Polyamines
KW - Receptors, Nicotinic
KW - Tyrosine
U2 - 10.1124/mol.64.4.954
DO - 10.1124/mol.64.4.954
M3 - Journal article
C2 - 14500752
SN - 0026-895X
VL - 64
SP - 954
EP - 964
JO - Molecular Pharmacology
JF - Molecular Pharmacology
IS - 4
ER -