Increases in intracellular calcium via activation of an endogenous P2‐purinoceptor in cultured CHO‐K1 cells

Abstract

1 Increases in intracellular calcium ([Ca²⁺]_i) were measured in Chinese hamster cultured ovary cells (clone, CHO-K1), by use of the fluorescent, calcium-sensitive dye, fura-2. 2 Addition of both ATP and UTP elicited rapid increases in [Ca²⁺]_i due to mobilization from intracellular stores and calcium entry across the plasma membrane. 3 Omission of calcium from the extracellular medium and pre-incubation with the inorganic calcium channel blocker, nickel (Ni²⁺) prevented the calcium entry components of the responses. 4 Investigation of the concentration-response relationships of various analogues of ATP suggests the presence of a purinoceptor which cannot be characterized as P_2X or P_2Y. In addition, there appears to be a sub-population of P_2Y-purinoceptors which do not cross-react with the ‘nucleotide’ receptor population. 5 Cross-desensitization and additivity experiments suggest that both ATP and UTP activate the same receptor. 6 Pre-incubation with the tumour-promoting agent, β-phorbol-12,13 dibutyrate (PDBu), caused a reduction in the increases in [Ca²⁺]_i, suggesting a role for protein kinase C in feedback inhibition of purinoceptor responses in this cell line. 7 In summary, we present evidence for the existence of an endogenous P_2U-purinoceptor (or ‘nucleotide receptor’) which is linked to increases in [Ca²⁺]_i in CHO-K1 cells.