Evolution of cAMP phosphodiesterase activity in cultured myometrial cells: effects of steroids and of successive subcultures.

Cyclic AMP phosphodiesterase (PDE) activity was characterized in culture of ewe myometrial cells and its sensitivity to steroid hormones was tested. Cultured myometrial cells were maintained from the first to the 20th subculture in the presence of 2% of serum in a medium supplemented with 1 microM of insulin. It was found that myometrial cells possess a PDE activity with atypical kinetics. The nonlinear responses in Lineweaver-Burke plots suggest the presence of high- and low-affinity PDE activities. In cell culture, apparent Km values were similar to those obtained from the original myometrium. Vmax values increased with successive subcultures, revealing an increase in the capacity of the cells to degrade cAMP; in parallel, the growth rate decreased. The PDE specific activity in cultured myometrial cells was inhibited by estradiol or progesterone. When added together, no synergistic effect was obtained. The rate of inhibition for both steroids was constant during successive passages for both low- and high-affinity conditions. Results obtained in myometrial cell long-term culture were compatible with reports in other species in vivo. Considering the role of cAMP in the regulation of uterine functions, subcultured myometrial cells provided us a useful experimental system with which to study the cAMP metabolism process.