Distribution of membrane-bound cyclic AMP-dependent protein kinase in plasma membranes of cells of the kidney cortex.

Renal cortical plasms membranes were separated by free flow electrophoresis into luminal (brush border microvilli) and contraluminal (basal-lateral membrane) fractions. These membranes were found to contain an intrinsic, self-phosphorylating system which consists of a cyclic AMP-dependent protein kinase, a phosphorprotein phosphatase and the substrate(s) of these enzymes. The kinase, but not the phosphatase, was stimulated by cyclic AMP; maximal (1.7-fold) stimulation was effected at a cyclic AMP concentration of 0.1 muM. The degree of phosphorylation of the brush borders was six times greater than that of the basal-lateral membranes in the absence of cyclic AMP and 2.3-fold greater in the presence of cyclic AMP. This preferential phosphorylation of the luminal membrane by membrane-associated protein kinase(s) may play a role in the parathyroid hormone-mediated alterations of solute reabsorption in the proximal tubule.