title: Mechanism of monensin-induced hyperpolarization of neuroblastoma-glioma hybrid NG108-15.
abstract: Addition of the ionophore monensin to mouse neuroblastoma-rat glioma hybrid NG108-15 cells leads to a 20 to 30-mV increase in the electrical potential across the plasma membrane as shown by direct intracellular recording techniques and by distribution studies with the lipophilic cation [3H]-tetraphenylphosphonium+ (TPP+) [Lichtshtein, D., Kaback, H.R. & Blume, A.J. (1979) Proc. Natl. Acad. Sci. USA 76, 650-654]. The effect is not observed with cells suspended in high K+ medium, is dependent upon the presence of Na+ externally, and the concentration of monensin that induces half-maximal stimulation of TPP+ accumulation is approximately 1 microM. The ionophore also causes rapid influx of Na+, a transient increase in intracellular pH, and a decrease in extracellular pH, all of which are consistent with the known ability of monensin to catalyze the transmembrane exchange of H+ for Na+. Although ouabain has no immediate effect on the membrane potential, the cardiac glycoside completely blocks the increase in TPP+ accumulation observed in the presence of monensin. Thus, the hyperpolarizing effect of monensin is mediated apparently by an increase in intracellular Na+ that acts to stimulate the electrogenic activity of the Na+,K+-ATPase. Because monensin stimulates TPP+ accumulation in a number of other cultured cell lines in addition to NG108-15, the techniques described may be of general use for studying the Na+,K+ pump and its regulation in situ.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002460:Cell Line; D005663:Furans / Q000494:pharmacology*; D005910:Glioma / Q000378:metabolism*; D006822:Hybrid Cells / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects*; D051379:Mice; D008985:Monensin / Q000494:pharmacology*; D009447:Neuroblastoma / Q000378:metabolism*; D009861:Onium Compounds / Q000378:metabolism; D009943:Organophosphorus Compounds; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology
chemical_list: D005663:Furans; D009861:Onium Compounds; D009943:Organophosphorus Compounds; D010042:Ouabain; D008985:Monensin; D012964:Sodium; D011188:Potassium; C013289:tetraphenylphosphonium