Electrophysiological analysis of
neuroblastoma X
glioma hybrid (NG108-15) cells was used as an in vitro neuronal model system to evaluate antagonists of the K+-selective carboxylic
ionophore,
nigericin. Changes in membrane electrical characteristics induced by
nigericin with and without the simultaneous administration of antagonists were measured using intracellular
microelectrode techniques. Bath application of
nigericin (3 microM) produced a severe hyperpolarization and blocked the generation of action potentials in response to electrical stimulation. Simultaneous administration of
nigericin plus the Na+-K+ pump inhibitor
ouabain or drugs known to influence Ca++ signaling in cells, i.e.,
quinidine, compound R24571,
verapamil or
haloperidol, was able to significantly attenuate the hyperpolarization. All antagonists acted in a concentration-dependent manner. However,
nigericin plus maximally effective concentrations of
ouabain (1 microM),
verapamil (3 microM) and
haloperidol (3 and 10 microM) resulted in moderate-to-severe depolarization by the end of 24 min. superfusions, suggesting that the concentrations of antagonists were excessive and that NG108-15 cell damage had occurred. In addition, none of the compounds studied was able to effectively prevent
nigericin-induced blockade of action potentials. Thus, none of these antagonists appears suitable for transition to in vivo antidotal protection studies.