The presence and properties of cyclic 3',5'-adenosine monophosphate phosphodiesterase (cAMP-PDIE) and cyclic 3',5'-guanosine monophosphate phosphodiesterase (cGMP-PDIE) were studied in glomeruli isolated from rat renal cortex by sieving and density gradient centrifugation. The specific activity of cGMP-PDIE was higher than the specific activity of cAMP-PDIE in glomeruli; in tubules and renal cortical slices, the specific activity of cAMP-PDIE was higher than that of cGMP-PDIE. In homogenates, x 100,000g supernate of homogenate (cytosol) and x 100,000g pellet (membrane fraction) from glomeruli, the specific activity of cGMP-PDIE was significantly higher than it was in analogous preparations from tubules or renal cortical slices. Cyclic 3',5'-GMP (10-6M to 10-5M) stimulated glomerular cAMP-PDIE, but it was without effect on cAMP-PDIE from tubules. Structural analogs of cyclic 3',5'-GMP or 5'-GMP did not stimulate glomerular cAMP-PDIE. Cyclic 3',5'-AMP slightly inhibited cGMP-PDIE from both glomeruli and tubules. N6-,2'-O-dibutyryl cyclic 3',5'-AMP inhibited cAMP-PDIE, but not cGMP-PDIE. The addition of calcium increased the activity of cGMP-PDIE, mainly in tubules, but was without effect on cAMP-PDIE. These results suggest the predominance of cyclic 3',5'-GMP catabolism in glomeruli in comparison with other cortical structures, and they demonstrate that both the specific activities and regulatory properties of cyclic nycleotide phosphodiesterase in glomeruli differ markedly from tubules or unfractionated renal cortical tissue.
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