Cytofluorimetric detection of intracellular phosphotyrosine in PDN12 (PNET) cell line. The dotted line (┈) represents phosphotyrosine in cells in serum-free condition for 24 hours. The solid line (—) shows the phosphotyrosine 10 minutes after stimulation with rhSCF (0.5 μg/10⁶ cells).