Protein kinase C activity in rat renal proximal tubule cells

The presence of protein kinase C (PKC) in proximal tubule cells of the rat kidney is established by means of immunodetection and by the demonstration of calcium-and phospholipid-dependent, staurosporine-inhibitable histone phosphorylation. The calcium-dependence of renal PKC is described. Maximal activation of the enzyme (178.2 and 258.8 pmol P₁ mg^-1 min^-1 for cytosol and membrane respectively) was achieved with 5 μM of Ca²⁺. Phorbol 12,13 dibutyrate (PDBu) translocated PKC from cytosol to membrane in a dose- and time-dependent fashion, while 4α-phorbol 12,13-didecanoate produced no significant effect on translocation. Cytosolic PKC activity was compared in immature and mature tissues (10- and 40-day-old kidneys). Basal activity was found to be significantly higher (P < 0.05) in immature cells (272.8 vs. 157.5 pmol P, mg^-1 min^-1). PDBu at 10^-6 M for 15 min reduced immunoreactivity in the soluble fraction of both groups, which was accompanied by a significant decrease in kinase activity. We speculate that the high PKC activity in the infant kidney plays a role in cell growth.