Fig. 4. Inhibition of MARCKS dephosphorylation by phosphatase inhibitors alters cell spreading. (A) The phosphorylation of MARCKS in myoblasts plated on fibronectin in the presence or absence of the phosphatase inhibitors, okadaic acid or microcystin. MARCKS phosphorylation was analyzed in untreated cells (lane 1), in cells treated with okadaic acid at 50 nM or 100 nM (lanes 2 and 3 respectively) and in cells treated with microcystin at 2 µM or 3 µM (lanes 4 and 5 respectively) 5 hours after cells were plated on fibronectin. (B) Prior to analysis of MARCKS phosphorylation in panel (A), cells were photographed (20x) to show the inhibition of spreading in the presence of 50 nM okadaic acid and 2 µM microcystin compared to untreated cells. Bar, 10 µm.