Reaction of tetraethylammonium with the open and closed conformations of the acetylcholine receptor ionic channel complex.

Abstract

A B S T R A C T The effect of tetraethylammonium (TEA) bromide on the neurally and iontophoretically evoked endplate current (EPC) of frog sartorius muscle was investigated using voltage-clamp and noise analysis techniques, and its binding to the acetylcholine (ACh) receptor ionic channel complex was determined on the electric organ of Torpedo oceUata. TEA (250-500 #M) produced an initial enhancement followed by a slow decline in the amplitude of the endplate potential and EPC, but caused only depression in the amplitude of the miniature endplate potential and current. In normal ringer's solution, the EPC current-voltage relationship was approximately linear, and the decay phase varied exponentially with membrane potential. Upon addition of 50-100 #.M TEA, the current-voltage relationship became markedly nonlinear at hyperpolarized command potentials, and with 250-2000 /~M TEA, there was an initial linear segment, an intermediate nonlinear segment, and a region of negative conductance. The onset of nonlinearity was dose-dependent, undergoing a 50 mV shift for a 10-fold increase in TEA concentration. The EPC decay phase was shortened by TEA at hyperpolarized but not depolarized potentials, and remained a single exponential function of time at all concentrations and membrane potentials examined. These actions of TEA were found to be independent of the sequence of polarizations, the length of the conditioning pulse, and the level of the initial holding potential. TEA shifted the power spectrum of ACh noise to higher frequencies and produced a significant depression of single channel conductance. The shortening in the mean channel lifetime agreed closely with the decrease in the EPC decay time constant. At the concentrations tested, TEA did not alter the EPC reversal potential, nor the resting membrane potential, and had little effect on the action potential duration. TEA inhibited the binding of both

The Action of Polymyxin B at the Frog Neuromuscular Junction

“…Recently the antibiotics, lincomycin and clindamycin, have been shown to alter miniature e.p.c. decay in a manner consistent with the drugs interacting with the acetylcholine-activated ionic channel (Fiekers, Marshall & Parsons, 1979 (Adler & Albuquerque, 1976;Adams, 1977;Adler et al, 1979;Lambert et al, 1979). Blockade of acetylcholine-activated channels by polymyxin B may explain the non-competitive nature of the antagonism to acetylcholine by polymyxin B reported by Viswanath & Jenkins (1978).…”

“…These data are consistent with the antibiotic having an action to block open acetylcholine-activated ionic channels as has been suggested for procaine (Adams, 1977), atropine (Alder & Albuquerque, 1976). tetraethylammonium (Alder, Oliveira, Albuquerque, Mansour & Eldefrawi, 1979) and lobeline (Lambert, Reynolds, Volle & Henderson, 1979). The Tls of e.p.cs recorded from endplates treated with glycerol (Magleby & Stevens, 1972), low concentrations of (+}tubocurarine (Katz & Miledi, 1978) or alpha bungartoxin (Katz & Miledi, 1978) and the T4 of untreated m.e.p.cs (Gage & McBurney, 1975) have been shown to vary with holding potential, becoming longer at more hyperpolarized potentials.…”

Muscarinic receptor is coupled with a cation channel through a GTP‐binding protein in guinea‐pig chromaffin cells.

“…Effects of TEA or Ba2+ on the muscarinic current Extracellular TEA has been found to suppress not only voltage-gated K+ channels (reviewed by Stanfield, 1983) but also the nicotinic cation channel at the frog endplate (TEA used at around 0-1 mM; Adler, Oliveira, Albuquerque, Mansoure & Eldefrawi, 1979). TEA (0-03-3 mM) was added to the standard bath solution, and the response to 1 /LM-oxotremorine was studied.…”

The interaction between hexamethonium and tubocurarine on the rat neuromuscular junction

“…piperocaine, quinacrine, histrionicotoxin) on the endplate (see Albuquerque et al, 1974;Adler et al, 1979;Tiedt et al, 1979;Adams & Feltz, 1980 a,b; Farley et al, 1981), for which the most usual explanation is binding to closed ionic channels, thus affecting the amplitude but not the time course of endplate currents. In summary, we suggest that the Tc reversal seen with C6 at the mammalian endplate results from (a) a competitive interaction at the receptors as postulated by Ginsborg & Stephenson (1974) and (b) a weak anticholinesterase effect.…”