INCREASES IN INTRACELLULAR CALCIUM VIA ACTIVATION OF AN ENDOGENOUS P(2)-PURINOCEPTOR IN CULTURED CHO-K1 CELLS

1 Increases in intracellular calcium ([Ca2+]i) were measured in chines e hamster cultured ovary cells (clone, CHO-Kl), by use of the fluoresc ent, calcium-sensitive dye, fura-2. 2 Addition of both ATP and UTP eli cited rapid increases in [Ca2+]i due to mobilization from intracellula r stores and calcium entry across the plasma membrane. 3 Omission of c alcium from the extracellular medium and pre-incubation with the inorg anic calcium channel blocker, nickel (Ni2+) prevented the calcium entr y components of the responses. 4 Investigation of the concentration-re sponse relationships of various analogues of ATP suggests the presence of a purinoceptor which cannot be characterized as P2X or P2Y. In add ition, there appears to be a sub-population Of P2Y-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-promo ting agent, beta-phorbol-12,13 dibutyrate (PDBu), caused a reduction i n 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 P2U-pu rinoceptor (or 'nucleotide receptor') which is linked to increases in [Ca2+]i in CHO-KI cells.