SPONTANEOUS FIRING OF NG108-15 CELLS INDUCED BY TRANSIENT EXPOSURE TOAMMONIUM-CHLORIDE

1. We report that NG108-15 (neuroblastoma x glioma) cells differentiat ed in defined serum-free media are capable of exhibiting stable automa ticity (the spontaneous occurrence of regenerative action potentials) following exposure to extracellular perfusates containing NH4Cl. 2. Me mbrane depolarization (4-5 mV) concomitant with an increased pH(i) dur ing NH4Cl exposure are followed by hyperpolarization (5-7 mV), subthre shold oscillations, and spontaneous firing after the removal of NH4Cl. 3. Cells cultured in 10% serum did not exhibit automaticity. Cells cu ltured in serum-free media are twice as likely to show automaticity as those cultured in reduced (1.5%) serum media. 4. We have examined fac tors that contribute to the events following NH4Cl exposure, namely, m embrane depolarization and hyperpolarization, subthreshold oscillation s, and automaticity, The inward currents activated at more negative po tentials and the ionic currents associated with pronounced afterhyperp olarization in NG108-15 cells cultured in serum-free media provide a b asis for the repetitive activity in general and automaticity in partic ular.