EFFECTS OF CYCLIC-NUCLEOTIDES AND SOME RELATED AGENTS ON P-32(1) LABELING OF RENAL POLYPHOSPHOINOSITIDES INVITRO

When rabbit kidney cortex slices were incubated in the presence of 32Pi and dibutyrylcyclic AMP (dbcAMP)4 a significant decrease in the labeling of phosphatidyl inositol phosphate (DPI) but not phosphatidyl inositol bisphosphate (TPI) was observed. In the presence of 0.3 mm caffeine cyclic AMP (cAMP) produced a similar effect. Caffeine potentiated the inhibitory effect of dbcAMP. At high concentrations (3 mm) caffeine alone decreased the 32Pi labeling of both DPI and TPI. These decreases in 32Pi labeling were not mediated by decreases in the labeling of intracellular Pi or ATP as measured by 10-min acid-labile nucleotide phosphate (10′-ALNP). Addition of cyclic GMP (cGMP) to the incubation medium decreased the labeling of DPI and to a lesser extent that of TPI also. Addition of parathyroid hormone (PTH) to the incubation medium (in the absence of exogenous cyclic nucleotides) also decreased the 32Pi labeling of DPI but not that of TPI. In contrast to the effects of cAMP, dbcAMP, cGMP, PTH, and caffeine, the addition of insulin to the incubation medium resulted in increased 32Pi labeling of DPI with no effect on TPI labeling. DPI isolated from kidney cortex slices prelabeled with 32Pi and subsequently incubated with cAMP or dbcAMP contained less label than DPI isolated from slices similarly prelabeled but subsequently incubated in the absence of either cAMP or dbcAMP. These data suggest an increased rate of DPI breakdown in the presence of elevated cAMP or dbcAMP concentrations. This hypothesis was supported by the fact that cAMP stimulated the hydrolysis of DPI but not of TPI by a polyphosphoinositide phosphodiesterase present in the supernatant fraction of rabbit kidney cortex. © 1979.