Regulation of cyclic GMP phosphodiesterase in the submandibular gland of adult rat.

Cyclic GMP phosphodiesterase was investigated in the submandibular gland of the adult rat to elucidate the regulatory mechanisms of cGMP concentration in this gland. Ca2+ sensitivity was easily demonstrated as in other tissues using EGTA in the buffer for elution from DEAE-cellulose. The presence of inhibitor proteins for basal and calmodulin-activated portions of Ca2+-dependent phosphodiesterase was suggested. The inhibitor for the basal activity of Ca2+-dependent phosphodiesterase was deemed to be a heat-labile protein, which decreased Vmax, but had no effect on the Km value for cGMP. The presence of more than one kind of inhibitor for the calmodulin-activated portion of the Ca2+-dependent phosphodiesterase was also suggested. One of these, which was not absorbed on DEAE-cellulose, was a heat-labile protein which caused an increase of Km for cGMP, but no change of Vmax.