Vol. 286, Issue 3, 1269-1276, September 1998

Potentiation and Inhibition of Nicotinic Acetylcholine Receptors by Spermine in the TE671 Human Muscle Cell Line¹

Zuoyi Shao, Ian R. Mellor, Matthew J. Brierley, John Harris and Peter N. R. Usherwood

Division of Molecular Toxicology, School of Biological Sciences, University of Nottingham, University Park, Nottingham, NG7 2RD, UK

Nicotinic acetylcholine receptors (nAChR) of the TE671 cell line were investigated using whole-cell and membrane patch recording techniques. At negative holding potentials (V_H), pulses of acetylcholine (ACh) elicited whole-cell inward currents that rapidly desensitized. The EC₅₀ value for ACh at V_H = 60 mV was 7.8 µM. The ACh-induced current reversed at ~0 mV. Desensitization of nAChR by ACh was biphasic and reversible within ~20 sec. Spermine (1-100 µM) potentiated responses to ACh (10 µM  1 mM) by reducing the rate of onset of desensitization; potentiation was inhibited by arcaine (10-100 µM). Spermine (1 mM) noncompetitively antagonized the AChinduced current. Antagonism by 1 to 5 mM spermine was voltage-dependent, increasing with negative V_H. In 100 µM arcaine, this antagonism was shown to contain a voltage-independent component. Spermine (10 mM) increased the EC₅₀ values for ACh, suggesting that at this concentration the polyamine is also a competitive antagonist. Single channel openings elicited during application of ACh to outside-out patches had a conductance of 47 pS at V_H = 60 mV. At 10 and 100 µM, spermine increased channel open probability (p_o), but at 1 mM spermine, p_o was not significantly different from controls. The single channel conductance for ACh was unaffected by 10 and 100 µM spermine, but was decreased by 1 mM spermine. Spermine promoted the occurrence of ~27 pS openings. It is proposed that spermine acts at an excitatory modulatory site similar to that present on N-methyl-D-aspartate receptors and at least three inhibitory sites on nAChR of TE671 cells.