Abstract 1. 1. Lymnaea neurons exhibit convulsive bursting behavior in solutions of Pentylenetetrazol (PTZ). 2. 2. Intracellular injection of Ca 2+ chelator, EGTA, causes bursting cells to return to more regular firing patterns. 3. 3. Experiments with calcium current blockers and 0 Ca-EGTA solution suggest that extracellular calcium is not necessary for the maintenance of PTZ-induced bursting. 4. 4. Experiments with CCmP, which causes release of mitochondrial calcium; and with taurine, which increases mitochondrial calcium binding, suggest that Ca 2+ from intracellular stores plays a role in PTZ-induced bursting.