Influence of cations on the electrical activity of neuroblastoma × glioma hybrid cells

Electrical excitability is one of the various neuronal properties of neuroblastoma × glioma hybrid cells. At a Ca²⁺ concentration of 1.8mM the action potential is inhibited by tetrodotoxin, suggesting that the inward current is carried by Na⁺ ions. In contrast, at a Ca²⁺ concentration of 20–36mM and even in the absence of Na⁺, spikes (sometimes repetitive) with strong hyperpolarizing afterpotential occur, which are no longer affected by tetrodotoxin. They are, however, blocked by antagonists of Ca²⁺ like La³⁺, Co²⁺, Mn²⁺, and the synthetic compounds D-600 and BAY a-1040. This seems to indicate that at high concentrations of Ca²⁺, the inward current of the action potential is essentially carried by Ca²⁺. Sr²⁺, but not Mg²⁺ can effectively substitute for Ca²⁺. It shows down the time course of the action potential. Ba²⁺ depolarizes the membrane gradually. If Ca²⁺ is also present, Ba²⁺ causes a reduced depolarization and spontaneous action potentials with no hyperpolarizing after-potential are observed.