Metabotropic Purinoreceptors in Rat Dorsal Horn Neurons: Predominantly Dendritic Location

Elevations of the cytosolic free Ca²⁺ concentration (Ca²⁺] _i ) in rat dorsal horn neurons induced by addition of ATP to the medium were compared in spinal cord slices and after isolation of the neurons. In slices, application of ATP results in an increase in the Ca²⁺] _i by 201 ± 12 nM, on the average; in a Ca²⁺ -free external solution the respective rise was 156 ± 14 nM (n = 45 of 76 examined cells), which indicate the presence of active purinergic metabotropic receptors in about 59% of the neurons. In freshly isolated neurons with absent dendrites, we found no metabotropic responses. Thus, the results confirm the conclusion on the localization of metabotropic postsynaptic purinoreceptors mostly on the dendritic tree of dorsal horn neurons.