In immature rat microvessels, endothelial cells and glioma cells, expo
sure to lead results in an increase in the level of protein kinase C i
n membranes. In this paper we have extended these studies to human ery
throcytes and, in addition, studied the phosphorylation of membrane pr
oteins. A significant increase in the phosphorylation of membrane cyto
skeletal proteins of molecular mass 120, 80, 52 and 45 kDa was observe
d in human erythrocytes treated for 60 min with lead acetate at concen
trations greater than 100 nM. These same proteins were phosphorylated
when erythrocytes were treated for 10 min with 50 nM phorbol 12-myrist
ate 13-acetate (PMA). Similarly, protein kinase C activity was elevate
d and an increase in the amount of protein kinase C-alpha was observed
in membranes from erythrocytes exposed to concentrations of lead acet
ate above 100 nM. No changes, however, in the activities of cAMP-depen
dent protein kinase, protein phosphatases I and IIA or casein kinase w
ere observed. Phosphorylation of the membrane proteins stimulated by l
ead acetate or by PMA was not observed in erythrocytes depleted of pro
tein kinase C by a 72-h treatment with 500 nM phorbol 12,13-dibutyrate
. Finally, no changes in the levels of calcium or diacylglycerol were
observed in erythrocytes stimulated with 100 nM lead acetate. These re
sults indicate that, in erythrocytes, lead acetate stimulates the phos
phorylation of membrane cytoskeletal proteins by a mechanism dependent
on protein kinase C. Since levels of calcium or diacylglycerols did n
ot increase, it appears that lead may activate the enzyme by a direct
interaction.