PI3K- and PLA2-independent chemotaxis in signal transduction mutants. (A) Chemotaxis to 1 μM cAMP was measured in 7-h starved cells in the absence (control) or presence of LY + BPB (PI3K and PLA2 inhibited). In wild-type cells and many mutants, LY + BPB does not inhibit chemotaxis by >15%, but in the guanylyl cyclase gc null and the cGMP target protein gbpc null cells, LY + BPB gives strong inhibition of chemotaxis. The asterisk indicates that the ipla null cells have a disrupted gene encoding the IP₃ receptor and were assayed in the presence of the PLC-inhibitor U23122 (10 μM) and EGTA (10 mM) to block Ca²⁺ uptake and intracellular release. ***, the difference with wild-type is significant at P < 0.001. (B) Chemotaxis was measured in 7-h starved cells toward different concentrations of cAMP. The results show that inhibition of PI3K and PLA2 or guanylyl cyclases lead to a mild inhibition of chemotaxis, whereas chemotaxis is strongly reduced when all three pathways are inhibited. The data presented are the means and SEM of at least three independent measurements.