Cyclic nucleotide phosphodiesterase in developing rat testis. Identification of somatic and germ-cell forms.

Several forms of phosphodiesterase are present in the male gonad, and their relative concentrations vary during testicular development. On the basis of kinetic analysis and chromatography on DEAE cellulose, 3 forms were separated: (a) a high-affinity cGMP phosphodiesterase, regulated by Ca2+ and calmodulin, similar to a form described in different tissues (peak I); (b) a high-affinity cAMP form insensitive to Ca2+, which cannot be readily compared with forms described elsewhere (peak II); and (c) a high-affinity cAMP phosphodiesterase, Ca2+- and calmodulin-insensitive, corresponding to the "hormone-regulated" form described in several systems (peak III). The elution pattern of peak I and calmodulin stimulation were dependent on free calcium concentration during cytosol preparation and chromatography. This datum and rechromatography in the presence or absence of excess calmodulin suggested that the enzyme complexes calmodulin in a Ca2+-dependent manner and is therefore activated. Moreover, whereas peak I was observed in all cell compartments of the testis, peak II was present in germ cells and peak III was found mainly in somatic cells. During development of the testis, a relevant enhancement in the ratio between cAMP and cGMP hydrolytic activity was observed together with an overall increase of phosphodiesterase activity, thus suggesting that the previously described increase in cAMP phosphodiesterase activity during testis maturation should be ascribed to forms present in both germ cells and somatic cells.