PHENYLARSINE OXIDE AND PHORBOL-MYRISTATE ACETATE INHIBIT THE CD3-INDUCED RISE OF CYTOSOLIC CA2+ IN JURKAT CELLS BY REFILLING INTERNAL CA2+ STORES

Phenylarsine oxide (PAO), an inhibitor of tyrosine phosphatases, has b een found to inhibit the early elevation in cytosolic Ca2+ concentrati on ([Ca2+](i)), related to the CD3 activation pathway in Jurkat T cell s. This inhibition was dose-dependent, consistent with previously repo rted effects of PAO on tyrosine phosphatases, and reversed by dimercap topropanol. By contrast, okadaic acid, an inhibitor of serine/threonin e phosphatases, had no effect on CD3-induced Ca2+ flux. PAO was compar ed with phorbol 12-myristate 13-acetate (PMA), which caused a similar, although less potent, inhibition as previously described. The two rea gents produced additive inhibition of the CD3-induced [Ca2+](i) rise, but did not affect thapsigargin- or ionomycin-driven Ca2+ flux in Jurk at cells. PAO and PMA prevented cells from complete depletion of intra cellular Ca2+ stores by an anti-CD3 monoclonal antibody (mAb) and rest ored, at least partially, the ionomycin-sensitive pool, when added aft er anti-CD3 mAb. Moreover, the CD3-induced inhibition of phosphatidyls erine synthesis, due tb depletion of internal Ca2+ stores, is reversed by PAO and PMA. Anti-phosphotyrosine immunoblot analysis show that th ese effects cannot be accounted for by an inhibition of CD3-induced ty rosine phosphorylations. We propose that PAO and, to a lesser extent, PMA allow the refilling of internal compartments by Ca2+, which conseq uently abrogates a capacitative entry of external Ca2+.