FACScan analysis of parental CMK cells treated with SCF with and without pretreatment with the Mek inhibitor, PD98059. CMK cells were analyzed by FACScan as described. Cells were gated to exclude nonviable cells using propidium iodine staining. (⋅⋅⋅⋅⋅) Represents the isotype control, (- - - - - - -) denotes the CMK cells treated with SCF and PD98059, (– – –) denotes the CMK cells treated with SCF alone. Staining with markers of megakaryocytic differentiation, CD41, or CD61 as indicated. The Mek inhibitor significantly decreased expression of both CD41 and CD61 (P < .001 comparing SCF with and without PD98059, by the Kolmogorov-Smirnov two sample test for both CD41 and CD61).