Abstract
The present study was undertaken to determine whether the nervous system specific protein S-100, whose function is, so far, unknown, could be involved in the regulation of neurotransmitter release from central nerve endings. Our results indicate that the exogenous protein was, by itself, unable to alter the spontaneous and the depolarization-induced release of neurotransmitters from rat brain synaptosomes. However, nanomolar concentrations of S-100 potentiated the effects of the Ca 2+ ionophore A23187 on the release of putative transmitter amino acids and catecholamines. The action of the S-100 protein seems to be related to its ability to promote, in combination with the ionophore, a higher influx of Ca 2+ into synaptosomes than that elicited by the ionophore alone. We hypothesize that the role of the S-100 present in nerve ending membranes might be that of facilitating the function of an endogenous, voltage-dependent Ca 2+ ionophore.
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