Fig. 3

Cross-desensitization among ATP, ADP and UTP in mice granulocytes. Granulocytes were loaded with the Ca²⁺ indicator fura-2. a–d Addition of ATP fully inhibited responses to ADP and UTP and vice-versa. e, f ADP and UTP showed full heterologous desensitization. g, h Thapsigargin, a Ca²⁺-ATPase inhibitor, which releases Ca²⁺ from intracellular stores, showed that the lack of a second response was not due to emptying of intracellular Ca²⁺ stores. i–l fMLP, another G-protein-coupled agonist, showed the specificity of cross-desensitization between ADP and UTP. m, n ATPγS did not promote heterologous desensitization to ADP and UTP response. o, p Lower concentration of ADP and UTP reduced responses to ADP and UTP. q, r MRS2179, a specific antagonist of the P2Y₁ receptor, inhibited responses to ADP but not to UTP. Granulocytes were pretreated for 30 min with MRS2179. All data are representative responses of at least four independent experiments