Inhibition of muscarinic receptor-mediated Ca27#x002B; mobilization by phorbol 12-myristate 13-acetate in chick embryo cells.

A muscarinic cholinergic receptor is present on undifferentiated cells of the chick embryo. Stimulation of the muscarinic receptor with muscarinic agonists triggers intracellular Ca2#x002B; mobilization. Here, we investigate the effect of phorbol 12-myristate 13-acetate (PMA) on the muscarinic receptor-mediated Ca2#x002B; mobilization, which is monitored in cell suspensions of chick embryos of stage 24 by chlorotetracycline fluorescence. PMA inhibits the Ca2#x002B; mobilization in a time-dependent and concentration-dependent manner without changing the ED50 of acetylcholine. The concentration of PMA that gives halfmaximal inhibition is 3.1×10-9 M PMA.