text: A broad-spectrum << phosphodiesterase >> (PDE) inhibitor ([[ 1,3-isobutyl-1-methylxanthine ]], 300 microM, n=6) and an ecto-phosphodiesterase inhibitor (1,3-dipropyl-8-p-sulfophenylxanthine, 1 mM, n=6) significantly attenuated cAMP-induced AMP secretion by 60 and 74%, respectively.