Activity of calcium/phospholipid dependent protein kinase during rat kidney development

The role of protein phosphorylation in renal amino acid transport

Changes in tubular reabsorption of amino acids and other solutes are characteristic of the immature renal tubule and of various hereditary nephropathies. The cellular mechanisms governing these aberrations in renal amino acid transport have not been established. Calcium (Ca2+)-dependent protein kinases are known to phosphorylate membrane-bound carrier proteins, thereby modulating transport of various solutes by the proximal tubule. The role of these enzymes in regulating renal tubular amino acid transport, particularly during kidney development, is unknown. We investigated: (1) the effect of Ca(2+)- and phospholipid-dependent protein kinase [protein kinase C (PKC)] and Ca2+/calmodulin-dependent protein kinase II (CaMKII) on sodium chloride (NaCl)-linked proline transport by renal brush border membrane vesicles (BBMV) from adult rats using the "hypoosmotic shock" technique (lysis of vesicles); (2) the activity, expression and subcellular distribution (cytosol, particulate, BBM) of Ca(2+)-dependent protein kinases in kidneys from 7-day-old and adult rats using MBP 4-14 and autocamtide II phosphorylation assays for PKC and CaMKII, respectively, endogenous protein phosphorylation (using gel electrophoresis and autoradiography) and Western immunoblot analysis to detect PKC and CaMKII. The studies showed: (1) endogenous (membrane-bound) CaMKII and PKC as well as exogenous, highly purified PKC inhibit proline uptake by phosphorylated, lyzed/resealed BBMV when compared with control vesicles; the voltage-clamped, nonelectrogenic component of proline transport was inhibited by PKC- but not CaMKII-mediated phosphorylation; (2) a Ca(2+)-dependent activity of both kinases was evident in all subcellular fractions tested in immature and adult kidneys.(ABSTRACT TRUNCATED AT 250 WORDS)

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 microM 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 less than 0.05) in immature cells (272.8 vs. 157.5 pmol Pi 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.

Time- and dose-dependent effects of protein kinase C on proximal bicarbonate transport

Activation of protein kinase C has been shown to cause both stimulation and inhibition of transport processes in the brush-border membrane and renal tubule. This study was designed to examine the dose-response nature and time-dependent effect of 4 beta-phorbol-12-myristate-13-acetate (PMA) on the rates of bicarbonate absorption (JHCO3) and fluid absorption (Jv) in the proximal convoluted tubule (PCT) of rat kidney. Bicarbonate flux was determined by total CO2 changes between the collected fluid and the original perfusate as analyzed by microcalorimetry. Luminal perfusion of PMA (10(-10) approximately 10(-5) M) within 10 min caused a significant increase of JHCO3 and Jv. A peaked curve of the dose response was observed with maximal effect at 10(-8) M PMA on both bicarbonate and fluid reabsorption, which could be blocked completely by amiloride (10(3) M) and EIPA (10(-5) M). On the other hand, with an increase of perfusion time beyond 15 min. PMA (10(-8) and 10(-6) M) could inhibit JHCO3 and Jv. Amiloride (10(-3) M) or EIPA (10(-5) M) significantly inhibits JHCO3 and Jv, while there is no additive effect of PMA and amiloride or EIPA on PCT transport. An inactive phorbol-ester, 4 alpha-phorbol, that does not activate protein kinase C, had no effects on JHCO3 and Jv. Capillary perfusion of PMA (10(-8) M) significantly stimulate both JHCO3 and Jv; however, PMA did not affect glucose transport from either the luminal side or basolateral side of the PCT. These results indicate that activation of endogenous protein kinase C by PMA could either stimulate or inhibit both bicarbonate and fluid reabsorption in the PCT dependent on time and dose, and these effects are through the modulation of Na+/H+ exchange mechanism.