Murine Macrophage Morphology Calcium Modulation of Phorbol Ester-induced Alterations in

The phorbol ester tumor promoter phorbol-12-myristate-13acetate (PMA) induced mouse resident peritoneal macrophage spreading in an in vitro system in a timeand dose-dependent manner; this process was modified by agents which alter intracellular calcium metabolism. After a 35-min incubation with PMA, 50% of the macrophages were spread (as classified by at least a 2-fold increase in cell surface area). Also at 35 min, the me dian effective concentration for PMA induction of spreading was 1.6 ng/ml. The intracellular calcium antagonist 8-(A/,A/-diethylamino)octyl-3,4,5-trimethoxybenzoate inhibited PMA-induced cell spreading with a one-half maximal inhibitory concentration of 8.0 UM. The calcium ionophore A23187 enhanced PMAinduced spreading by 30% at 0.1 to 10 nw. The histological dye ruthenium red, which purportedly increases intracellular calcium by displacing membrane-bound calcium stores, enhanced PMAinduced spreading up to 75% at 1.0 pw. The cationic chelator ethyleneglycolbis(/i-aminoethylether)-A/,A/-tetraacetic acid (1.8 and 3.6 HIM) had no effect on PMA-induced spreading. Thus, PMA-induced spreading was independent of extracellular cal cium but was modulated by agents altering intracellular calcium metabolism. Microfilament formation, a proposed mechanism of cell spreading, also depends on intracellular calcium availability. The microfilament inhibitor cytochalasin B inhibited PMA-induced spreading with a one-half maximal inhibitory concentration of 1 /¿M. Future experiments should investigate the hypothesis that calcium availability to the cytoskeletal elements regulates the morphological effects of PMA on macrophages.