Ca(2+)-dependent protein kinases modulate proline transport across the renal brush-border membrane

The cellular mechanisms controlling reabsorption of amino acids in the renal proximal tubule are unknown. Ca(2+)-dependent protein kinases modulate the activity of several ion channels and carriers in the kidney. The role of these enzymes in regulating tubular amino acid transport has not been established. We investigated the effect of Ca(2+)- and phospholipid-dependent protein kinase C (PKC) and Ca2+/calmodulin-dependent protein kinase II (CaMK II) on Na(+)- and Cl(-)-dependent proline transport across the rat renal brush-border membrane (BBM). Bioassays utilizing selective peptide substrates for Ca(2+)-dependent protein kinases demonstrated the presence of PKC and CaMK II in the BBM. Renal brush-border membrane vesicles (BBMV) were phosphorylated using the "hyposmotic shock" technique. Endogenous (membrane-bound) CaMK II and PKC, as well as exogenous, highly purified PKC inhibited NaCl-linked proline uptake by phosphorylated, lysed/resealed BBMV compared with control vesicles. The inhibitory effect of Ca2+ on proline transport, without the presence of other kinase activators, was mediated by activation of endogenous CaMK II. The CaMK II- and PKC-induced inhibition of proline uptake was reversed by the specific kinase inhibitor peptides CaMK II-(281-302) and PKC-(19-31), respectively. These data suggest that Ca(2+)-dependent protein kinase-mediated phosphorylation inhibits NaCl-dependent proline transport across the tubular luminal membrane.