Characteristics of K⁺- and veratridine-induced release of ATP from synaptosomes prepared from dorsal and ventral spinal cord

K⁺ and veratridine released 2-3 times more ATP from dorsal than from ventral spinal cord synaptosomes (P₂). K⁺-induced release of ATP was Ca²⁺-dependent whereas veratridine-induced release was augmented in a Ca²⁺-free medium. Twenty-one to 24 days after section of the right sciatic nerve of the rat the evoked release of ATP from right dorsal synaptosomes was indistinguishable from release from left dorsal synaptosomes. Although these latter results suggest that ATP may not be a transmitter at primary afferent synapses in the spinal cord, it is possible that sciatic nerve section does not deplete the releasable pool of ATP in primary afferent terminals or that ATP is also released from interneurons in the dorsal spinal cord.