Calcium-Dependent Action Potentials in Leech Giant Salivary Cells

Two pairs of discrete salivary glands are located at the base of the muscular proboscis of the sanguivorous Glossiphoniid leeches Haementeria ghilianii and Haementeria officinalis. Each anterior gland is 0.8 cm to 2 cm in length, and comprises over 200 giant salivary cell bodies ranging from 150 microns to over 1000 microns in diameter, depending on the size of the animal. The salivary cells are neither electrically nor dye coupled, and there is no acinar structure or common duct, but instead each cell extends an individual ductule. The cells fire action potentials of 100–200 ms duration and 70–100 mV amplitude in response to depolarizing pulses, or at the cessation of a hyperpolarizing pulse. The impulse is abolished by procedures known to antagonize calcium currents, and persists in sodium-free solution, or when calcium is replaced with strontium or barium. Our results support the hypothesis of a purely calcium-dependent impulse.