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

Abstract

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. 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. 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. Investigation of the concentration‐response relationships of various analogues of ATP suggests the presence of a purinoceptor which cannot be characterized as P2X or P2Y. In addition, there appears to be a sub‐population of P2Y‐purinoceptors which do not cross‐react with the ‘nucleotide’ receptor population. Cross‐desensitization and additivity experiments suggest that both ATP and UTP activate the same receptor. 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. In summary, we present evidence for the existence of an endogenous P2U‐purinoceptor (or ‘nucleotide receptor’) which is linked to increases in [Ca2+]i in CHO‐K1 cells. 1993 British Pharmacological Society