Inhibition of muscarinic receptor-mediated Ca 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 Ca mobilization. Here, we investigate the effect of phorbol 12-myristate 13-acetate (PMA) on the muscarinic receptor-mediated Ca mobilization, which is monitored in cell suspensions of chick embryos of stage 24 by chlorotetracycline fluorescence. PMA inhibits the Ca mobilization in a time-dependent and concentration-dependent manner without changing the ED of acetylcholine. The concentration of PMA that gives halfmaximal inhibition is 3.1×10 M PMA.