ATP induces Ca²⁺ release from IP₃-sensitive Ca²⁺ stores exclusively in large DRG neurones

Purinoreceptor-mediated intracellular Ca²⁺ release was studied in freshly isolated adult mouse dorsal root ganglia (DRG) neurones. The cytoplasmic Ca²⁺ concentration ([Ca²⁺](i)) was measured using indo-1- based microfluorimetry. The application of 100 μM ATP in Ca²⁺-free solution triggered an increase in [Ca²⁺](i) in 93% of large DRG neurones but in no small ones. The ATP-induced [Ca²⁺](i) transients in large neurones were inhibited by cells incubation with thapsigargin or by intracellular dialysis with heparin-containing solution. The ATP-triggered increase in [Ca²⁺](i) was not mimicked by adenosine and was blocked by suramin, suggesting the involvement of metabotropic (P(2Y)) purinoreceptors. We conclude that large (proprioceptive) DRG neurones express P(2Y) purinoreceptors linked to the inositol 1,4,5-triphosphate-Ca²⁺ intracellular signal transduction cascade, whereas small (nociceptive) DRG neurones are devoid of such a mechanism.