Intracellular calcium concentration during pentylenetetrazol-induced bursting activity in snail neurons

To clarify the role of intracellular free calcium in the provocation of bursting activity, the intracellular calcium concentration was measured using calcium-sensitive microelectrodes during pentylenetetrazol (PTZ)-induced bursting activity in snail neurons. In the PTZ-sensitive neurons of the snail, Euhadra peliomphala, the intracellular calcium concentration was higher than that in the normal state during PTZ-induced bursting activity, but lower than that which induced the calcium-activated potassium conductance elevation. By application of 50 microM calcium ionophore, A23187, a slight increase in intracellular calcium concentration with a slight depolarization occurred. Then a greater increase of intracellular calcium concentration with bursting activity was observed. By application of 100 microM A23187, a rapid and intense increase of intracellular calcium concentration with hyperpolarization was observed. These findings suggest that, for the provocation of bursting activity, sustained elevation of the intracellular calcium concentration, higher than that in the normal state but lower than that which evokes calcium-activated potassium conductance elevation, is required.