Intracellularly injected aequorin detects transmembrane calcium flux during action potentials in an identified neuron from the terrestrial slug, Limax maximus

The abdominal ganglion of the terrestrial slug, Limax maximus, contains several large identifiable neurons. The largest abdominal giant cell (AGC) is a pacemaker neuron. Its rhythmic spontaneous activity is not dependent on synaptic input and can be reset by intracellularly applied current pulses. Action potentials can occur spontaneously or be elicited in the absence of either sodium or calcium in the external medium. Aequorin injected into the AGC luminesces in response to individual, spontaneously produced action potentials. The onset of light output occurs before the peak depolarization of the action potential. These results provide convincing evidence for transmembrane calcium flux during action potentials in this neuron.