ATP AND UTP ACTIVATE CALCIUM-MOBILIZING P-2U-LIKE RECEPTORS AND ACT SYNERGISTICALLY WITH INTERLEUKIN-1 TO STIMULATE PROSTAGLANDIN E-2 RELEASE FROM HUMAN RHEUMATOID SYNOVIAL-CELLS

Objective. To pharmacologically and functionally characterize calcium- mobilizing purine receptors on adherent human rheumatoid synovial cell s. Methods. Fura-2-loaded synovial cells were screened for changes in cytosolic calcium concentration after the addition of purine receptor agonists. Release of interleukin-1 (IL-1) and prostaglandin E-2 (PGE(2 )) was assessed by enzyme-linked immunosorbent assay (ELISA) and radio immunoassay, respectively. The effect of IL-1 prestimulation on purine -mediated PGE(2) release was determined. Results, ATP (1-100 mu M) and UTP (1-100 mu M), but not 2-methylthio-ATP or adenosine, stimulated m obilization of calcium from intracellular stores in synovial cells. AT P and UTP stimulated a small. but significant, increase in PG release from resting synoviocytes and a dramatic increase in PG release from s ynoviocytes prestimulated with recombinant human IL-1 alpha. Neither A TP nor UTP stimulated synoviocyte release of IL-1 as measured by speci fic ELISA. The effects of ATP and UTP on PG secretion were mimicked by phorbol 12-myristate 13-acetate and thapsigargin, and blocked by BAPT A buffering of cytosolic calcium. Conclusion. Adherent human rheumatoi d synovial cells mobilize intracellular calcium via a P-2U-like purine receptor. P-2U receptor agonists stimulate PGE(2) release from synovi ocytes, an effect that is greatly enhanced by IL-1 alpha prestimulatio n and blocked by intracellular calcium buffering.