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 P(i) mg-1 min-1 for cytosol and membrane respectively) was achieved with 5-mu-m of Ca2+. Phorbol 12,13 dibutyrate (PDBu) translocated PKC from cytosol to membrane in a dose- and time-dependent fashion, while 4-alpha-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(i) 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.