Spontaneous firing of NG108-15 cells induced by transient exposure to ammonium chloride

1. We report that NG108-15 (neuroblastoma x glioma) cells differentiated in defined serum-free media are capable of exhibiting stable automaticity (the spontaneous occurrence of regenerative action potentials) following exposure to extracellular perfusates containing NH₄Cl. 2. Membrane depolarization (4-5 mV) concomitant with an increased pH, during NH₄Cl exposure are followed by hyperpolarization (5-7mV), subthreshold oscillations, and spontaneous firing after the removal of NH₄Cl. 3. Cells cultured in 10% serum did not exhibit automaticity. Cells cultured in serum- free media are twice as likely to show automaticity as those cultured in reduced (1.5%) serum media. 4. We have examined factors that contribute to the events following NH₄Cl exposure, namely, membrane depolarization and hyperpolarization, subthreshold oscillations, and automaticity. The inward currents activated at more negative potentials and the ionic currents associated with pronounced after hyperpolarization in NG108-15 cells cultured in serum-free media provide a basis for the repetitive activity in general and automaticity in particular.