CYCLIC AMP-DEPENDENT PROTEIN KINASE ACTIVITY AND ENDOGENOUS PROTEIN PHOSPHORYLATION IN ISOLATED CORTICAL SEGMENTS OF RABBIT NEPHRON

Abstract Cyclic AMP-dependent protein kinase activity and endogenous protein phosphorylating activity are reported for 6 cortical segments of the rabbit nephron which were microdissected and collected according to their morphology. The 6 cortical nephron segments, namely the glomerulus (Glm), proximal convoluted tubule (PCT), proximal straight tubule (PST), cortical ascending limb of Henle’s loop (CAL), distal convoluted tubule (OCT), and cortical collecting tubule (CCT), showed protein kinase activities which were increased 1.8-4,9 fold by 10-6 M cyclic AMP in the presence of histone MA, histone f2b or histone f3 as a protein substrate. However, all these segments showed little or no cyclic AMP dependent increase of activity with either protamine or α-casein as a protein substrate. Cyclic AMP increased the endogenous protein phosphorylation of Glm (10-6 M cyclic AMP), of CAL (10-7 and 10-8 M cyclic AMP), of DCT (10-6 M cyclic AMP) and of CCT (10-5, 10-7 and 10-6 M cyclic AMP). In contrast. PCT showed decreased endogenous protein phosphorylation in the presence of 10-7,10-5 and 10-4 M cyclic AMP.