TY - JOUR T1 - Contrasting Actions of Philanthotoxin-343 and Philanthotoxin-(12) on Human Muscle Nicotinic Acetylcholine Receptors JF - Molecular Pharmacology JO - Mol Pharmacol SP - 954 LP - 964 DO - 10.1124/mol.64.4.954 VL - 64 IS - 4 AU - Tim J. Brier AU - Ian R. Mellor AU - Denis B. Tikhonov AU - Ioana Neagoe AU - Zuoyi Shao AU - Matt J. Brierley AU - Kristian Strømgaard AU - Jerzy W. Jaroszewski AU - Povl Krogsgaard-Larsen AU - Peter N. R. Usherwood Y1 - 2003/10/01 UR - http://molpharm.aspetjournals.org/content/64/4/954.abstract 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 μM 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 μM PhTX-343 significantly reduced the mean open time of channel openings evoked by 1 μM 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 μM 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 μM 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. ER -