Adenosine 3' :5' -monophosphate-dependnet phosphorylations of renal subcellular fractions. Differences between cortical and medullary membrane preparations.

Electrophoretic patterns of phosphorylated components from kidney cortical and medullary plasma membranes show clear differences. Radioautography of a dried-slab sodium dodecyl sulfate (SDS)-polyacrylamide gel reveals that at least 18 phosphorylated components can be resolved from cortical membranes after incubation with 5 PM [Y-~‘P]ATP. Fifteen components are resolved from medullary membranes. Among conspicuous differences in the patterns are a 94,000 component which is largely confined to cortical membranes and an 88,000 component that is only detected in the medullary membranes. Most relevant, CAMP enhances “P incorporation 2to 4-fold into two to four components from cortical membranes of apparent molecular weights of 72,000 to 84,000. This pattern is observed by both the radioautographic procedure and by “‘P counting of sliced SDS-acrylamide gels. Half-maximal stimulation of the phosphorylation reaction occurs at 1.4 x 10m7 M CAMP. The effect of CAMP is on the K,,, for ATP rather than on maximal velocity of the phosphorylation reaction. In marked contrast to results with cortical membranes, CAMP has no significant effect on “P incorporation into medullary membranes. These results suggest that CAMP-mediated hormone responses in the kidney cortex may involve membrane phosphorylation(s). However, CAMP-mediated hormone responses in the medulla do not involve membrane phosphorylations. Hormone action in this region may involve phosphorylation of specific cytosol proteins.