Phototransduction in aplysia neurons: calcium release from pigmented granules is essential.

Increased free intracellular calcium mediates increased membrane potassium conductance in illuminated Aplysia giant neurons. The calcium source was examined by microprobe analysis of cytoplasmic pigmented granules. Illumination markedly depleted granules of calcium and altered them structurally. Release of calcium from granules is essential for phototransduction.