Altered expression of cyclic nucleotide phosphodiesterase isozymes during culture of aortic endothelial cells

Primary cultures of bovine aortic endothelial cells (BAEC) express cyclic nucleotide phosphodiesterase (CN PDE) isozymes of the PDE2, PDE4 and PDE5 gene families. We report here that the isozyme profiles of CN PDE and the amounts of each vary with the passage number of BAEC cultures. Characterization by anion-exchange chromatography and pharmacological criteria were used to study CN PDE in early (4-6), intermediate (6-10), and late (> 17) passages of purified BAEC. PDE2 and a minor fraction of PDE5 accounted for cyclic GMP hydrolysis in early passages, but both isozymes were lost with cell passage. Cyclic AMP was hydrolyzed by both PDE2 and PDE4 isozymes in early passage endothelial cells, but PDE4 was increased dramatically in higher passage cells. Also appearing in the higher passage cells were prominent PDE1 and minor PDE3 activities. The ratios of cytosolic to particulate activities were similar at all passages. BAEC PDE isoforms in intact cells assessed by [3H]-adenine prelabeling showed that atriopeptin II decreased isoproterenol-induced cyclic AMP accumulation in early but not later passage cells, consistent with the loss of PDE2 expression. Enhancement of isoproterenol-induced cyclic AMP accumulation by rolipram, a PDE4 inhibitor, was also greatly diminished during culture passages. Changes in CN PDE isoform expression and consequent cyclic AMP turnover validate the importance of considering cell passage number when cultures of BAEC are used to study the regulation of endothelial cell cyclic nucleotide metabolism and processes mediated by cyclic nucleotides in this model system.