Hormonally sensitive cyclic AMP phosphodiesterase in liver cells. An ecto-enzyme

Ecto-cyclic AMP phosphodiesterase activity was determined from freshly isolated and cultured liver cells. The cells were capable of hydrolyzing cyclic AMP in the medium. The ecto-phosphodiesterase represents a low Km phosphodiesterase which was activated by physiological concentrations of insulin. The product, 5'-AMP, was recovered in the medium and not with the cells. The enzyme was inhibited with aminophylline and trypsin. The ecto-phosphodiesterase activity was proportional to cell number, and total phosphodiesterase activity increased 5- to 10-fold when the cells were ruptured. About one-third of the ecto-phosphodiesterase activity from freshly isolated liver was due to phosphodiesterase in the medium. No phosphodiesterase was in the medium of cultured liver cells.