LEUKOTRIENE-D4 INDUCED CALCIUM CHANGES IN U937 CELLS MAY UTILIZE MECHANISMS ADDITIONAL TO INOSITOL PHOSPHATE PRODUCTION THAT ARE PERTUSSIS TOXIN INSENSITIVE BUT ARE BLOCKED BY PHORBOL-MYRISTATE ACETATE

DMSO differentiated U937 cells responded to 10(-6) M LTD4, LTB4 and FMLP with an increase in both InsP formation and [Ca2+]i. FMLP caused a greater rise in InsPs than either LTD4 or LTB4, which were equivalent. LTD4, however, caused a greater increase in [Ca2+]i than LTB4 (4-fold) or FMLP. The FMLP [Ca2+]i and InsP responses were abolished by pertussis toxin (100 ng/ml for 4 h) but were unaffected by PMA (10(-7) M for 3 min). In contrast, the LTD4 [Ca2+]i and InsP responses were reduced by only 50% by pertussis toxin, whilst PMA reduced the [CA2+]i and InsP responses to LTD4 by 75 and 30%, respectively. These results suggest that mechanisms additional to InsP formation exist for mediating LTD4 evoked increases in ]Ca2+[i.