K252b is an indolocarbazole isolated from the actinomycete Nocardiopsis, first described as an inhibitor of protein kinase C. However, as this compound does not freely pass through the cell membrane, it is used to inhibit extracellular kinases (ectokinases) of cells in culture. K252b inhibits receptor-mediated degranulation from basophil-like RBL-2H3 cells (IC50 = 0.5 μg/ml) and human basophils. This extracellular inhibitor is also used in comparison studies with the closely related, cell-permeable inhibitor K252a, particularly in studies of neuronal differentiation.
