Activity-dependent accumulation of Ca2+ in axon and dendrites of the leech Leydig neuron

We have investigated Ca2+ changes evoked by single action potentials (APs) in axon and dendrites of leech Leydig neurons. Dendritic Ca2+ transients induced by an AP were twice as large as in the axon, and Ca2+ recovery was significantly faster in the dendrites as compared to the axon. The AP-induced Ca2+ transients were blocked by Co2+ and suppressed in Ca2+-free saline, indicating Ca2+ influx through voltage-activated channels. During a train of APs, Ca2+ accumulated significantly more in the axon than in the dendrites. Suppression of the Ca2+ influx changed the shape of the action potential and increased the firing frequency. The results suggest a functional role of Ca2+ influx and Ca2+ accumulation during electrical activity in different neuronal subcompartments.