CA2-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. Ca2+-dependent protein kinases mod ulate 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 Ca2+- and phos pholipid-dependent protein kinase C (PKC) and Ca2+/calmodulin-dependen t protein kinase II (CaMK II) on Na+- and Cl--dependent proline transp ort across the rat renal brush-border membrane (BBM). Bioassays utiliz ing selective peptide substrates for Ca2+-dependent protein kinases de monstrated the presence of PKC and CaMK II in the BBM. Renal brush-bor der membrane vesicles (BBMV) were phosphorylated using the ''hyposmoti c shock'' technique. Endogenous (membrane-bound) CaMK II and PKC, as w ell as exogenous, highly purified PKC inhibited NaCl-linked proline up take by phosphorylated, lysed/resealed BBMV compared with control vesi cles. The inhibitory effect of Ca2+ on proline transport, without the presence of other kinase activators, was mediated by activation of end ogenous CaMK II. The CaMK II- and PKC-induced inhibition of proline up take was reversed by the specific kinase inhibitor peptides CaMK II-(2 81-302) and PKC-(19-31), respectively. These data suggest that Ca2+-de pendent protein kinase-mediated phosphorylation inhibits NaCl-dependen t proline transport across the tubular luminal membrane.