Isozymes of cyclic-3', 5'-nucleotide phosphodiesterases in renal epithelial LLC-PK1 cells

Isozymes of cyclic-3′,5′-nucleotide phosphodiesterases in renal epithelial LLC-PK 1 cells. Metabolism of cAMP and cGMP by the major types (families) of cyclic-3′,5′-nucleotide phosphodiesterases (PDE) was studied in confluent renal epithelial LLC-PK 1 cells grown in vitro. LLC-PK 1 cells mainly contain the cAMP-specific rolipram-sensitive PDE type-IV (PDE-IV), the Ca 2+ -calmodulin dependent PDE type-I and cGMP-specific PDE type-V; all these PDEs are mainly localized in cytqsol. Analysis of PDE activities in soluble extract of LLC-PK 1 cell homogenate by FPLC ionex chromatography on Mono-Q column also disclosed the presence of low activities of cGMP-stimulated PDE-II and PDE-III. Moreover, activity of PDE-IV was resolved into four distinct chromatographic peaks. The increase of cAMP level in response to incubation of intact LLC-PK 1 cells with vasopressin (AVP) was markedly enhanced in the presence of rolipram, but not in the presence of other PDE isozyme-specific inhibitors. Incubation with AVP and atrio-peptin (ANP) together resulted in increase in cGMP and a small decrease of cAMP accumulation in LLC-PK 1 cells. Results of these studies first show that the LLC-PK 1 cells contain all five major types of PDE isozymes where PDE-IV, PDE-I and PDE-V are quantitatively predominant. The rolipram-sensitive PDE-IV, present in several chro-matographically distinct forms, appears to be the key PDE isozyme involved in control of cAMP generated in response to stimulation by AVP in LLC-PK 1 cells.