S-100-IMMUNOREACTIVE PROTEIN IN HELIX NEURONS

S-100 proteins are a versatile group of calcium-binding proteins which exert intracellular as well as extracellular functions in a variety o f cells. Our immunocytochemical studies, using the central nervous sys tem of the terrestrial wail, Helix pomatia, showed that S-100-like mat erial is present exclusively in a restricted number of neurons distrib uted in the cerebral ganglia, the left parietal ganglion, and the visc eral ganglion. Electrophysiological investigations showed that immunos tained neurons spontaneously discharge action potentials in a beating or bursting mode. Voltage clamp experiments further revealed a pronoun ced N-shaped current-voltage relationship of outward currents, indicat ing a prominent calcium-activated potassium current in these cells. Ex tracellular application of the disulfidic form of S-100(s-s) results i n suppression of spontaneous discharge activity accompanied by an incr ease of membrane conductance. The total outward current as well as the inward rectifier current were increased. After removal of the calcium -dependent outward current component, S-100 effects ware abolished ind icating that S-100 acts an the calcium-activated current component. Ou r results suggest that S-100-like proteins modulate electrical activit y of neurons in the central nervous system of Helix pomatia.