Cyclic Nucleotide Phosphodiesterase Activity in Human Peripheral Blood Lymphocytes and Monocytes

Abstract

cAMP and cGMP phosphodiesterase (PDE) activity was assayed in human peripheral blood lymphocytes purified by isopycnic centrifugation as well as in lymphocyte preparations further purified to remove contaminating platelets and monocytes. The 16,000 × G supernatant from sonicates of each of these cell preparations contained two hydrolytic activities for cAMP with apparent K_m of 1.1 to 2.5 µM and 33 to 66 µM, and a single hydrolytic activity for cGMP with an apparent K_m of 6 to 25 µM. When lymphocytes were disrupted by Dounce homogenization, there was only a single, low K_m cAMP PDE activity in the homogenate; however, the 16,000 × G supernatant demonstrated 2 K_m similar to that seen in sonicated lymphocytes. Treatment of the Dounce preparations with 0.5% Triton X-100 or 1.0% NP-40 converted these preparations to activities similar to those seen in sonicated preparations. cGMP hydrolytic activity was low or absent in the Dounce preparations and was not altered by centrifugation; however, it was markedly enhanced by detergent extraction. These data indicate that human peripheral blood lymphocytes and monocytes have PDE activities similar to those seen in other tissues.