Potentiation and inhibition of nicotinic acetylcholine receptors by spermine in the TE671 human muscle cell line.
Nicotinic acetylcholine receptors (nAChR) of the TE671 cell line were investigated using whole-cell and membrane patch recording techniques. At negative holding potentials (VH), pulses of acetylcholine (ACh) elicited whole-cell inward currents that rapidly desensitized. The EC50 value for ACh at VH = -60 mV was 7.8 microM. The ACh-induced current reversed at approximately 0 mV. Desensitization of nAChR by ACh was biphasic and reversible within approximately 20 sec. Spermine (1-100 microM) potentiated responses to ACh (10 microM - 1 mM) by reducing the rate of onset of desensitization; potentiation was inhibited by arcaine (10-100 microM). Spermine (1 mM) noncompetitively antagonized the AChinduced current. Antagonism by 1 to 5 mM spermine was voltage-dependent, increasing with negative VH. In 100 microM 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 VH = -60 mV. At 10 and 100 microM, spermine increased channel open probability (po), but at 1 mM spermine, po was not significantly different from controls. The single channel conductance for ACh was unaffected by 10 and 100 microM spermine, but was decreased by 1 mM spermine. Spermine promoted the occurrence of approximately 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.
Shao
Z
Z
Division of Molecular Toxicology, School of Biological Sciences, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
Mellor
I R
IR
Brierley
M J
MJ
Harris
J
J
Usherwood
P N
PN
D000109:Acetylcholine / Q000494:pharmacology; D001645:Biguanides / Q000494:pharmacology; D002460:Cell Line; D004357:Drug Synergism; D006801:Humans; D009132:Muscles / Q000187:drug effects; D011978:Receptors, Nicotinic / Q000187:drug effects*; D013096:Spermine / Q000494:pharmacology*
D001645:Biguanides; D011978:Receptors, Nicotinic; D013096:Spermine; C006624:arcaine; D000109:Acetylcholine