Changes in cAMP phosphodiesterase activity during oral mucosal regeneration

Preliminary studies (Lineweaver-Burk, Ca2+ calmodulin sensitivity) suggest that oral mucosa contains at least two cyclic AMP phosphodiesterases, one a high affinity (low Km) enzyme and the other a low affinity (high Km) enzyme. Analysis of the distribution of both enzymatic forms during oral mucosal regeneration revealed that the low Km, and high Km cAMP phosphodiesterase activities were significantly elevated prior to the first wave of cAMP accumulation and during the second cAMP wave. Although the cAMP peaks declined between 20-24 h, both cAMP phosphodiesterases remained significantly elevated at the wound site. The apparent Km of the low Km form increased from 5.3 to 7.5 microM, while that of the high Km form remained essentially unaltered 20 h after wounding. The low Km, and high Km cAMP phosphodiesterase activities in normal rat oral mucosa were not affected by epinephrine or insulin; were slightly inhibited by glucagon, and significantly inhibited by methylprednisolone. Imidazole and histamine activated both forms and theophylline was inhibitory to the enzyme. The high Km cAMP phosphodiesterase was sensitive, and the low Km form insensitive to Ca2+ calmodulin stimulation.