Fig. 4. Immunolocalization of protein kinase C (PKC)-α. In untreated cells, PKC-α was detected in the cytoplasm ( A ). Treatment with phorbol 12-myristate 13-acetate caused translocation of PKC-α from cytoplasm to membrane ( B ). Treatment with acetylcholine also induced translocation of PKC-α to membrane ( C ). The muscarinic receptor antagonist, atropine, alone had no effect on the subcellular distribution of PKC-α compared with unstimulated cells ( D ). However, pretreatment of pulmonary venous smooth muscle cells with atropine before acetylcholine treatment abolished the acetylcholine-induced translocation of PKC-α ( E ).