Abstract: | 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. |