Cyclic expression of endothelin-converting enzyme-1 mediates the functional regulation of seminiferous tubule contraction

The potent smooth muscle agonist endothelin-l (ET-1) is involved in the loc al control of seminiferous tubule contractility, which results in the forwa rd propulsion of tubular fluid and spermatozoa, through its action on perit ubular myoid cells. ET-1, known to be produced in the seminiferous epitheli um by Sertoli cells, is derived from the inactive intermediate big endothel in-l (big ET-1) through a specific cleavage operated by the endothelin-conv erting enzyme (ECE), a membrane-bound metalloprotease with ectoenzymatic ac tivity. The data presented suggest that the timing of seminiferous tubule c ontractility is controlled locally by the cyclic interplay between differen t cell types. We have studied the expression of ECE by Sertoli cells and us ed myoid cell cultures and seminiferous tubule explants to monitor the biol ogical activity of the enzymatic reaction product. Northern blot analysis s howed that ECE-1 (and not ECE-2) is specifically expressed in Sertoli cells ; competitive enzyme immunoassay of ET production showed that Sertoli cell monolayers are capable of cleaving big ET-1, an activity inhibited by the E CE inhibitor phosphoramidon. Microfluorimetric analysis of intracellular ca lcium mobilization in single cells showed that myoid cells do not respond t o big endothelin, nor to Sertoli cell plain medium, but to the medium condi tioned by Sertoli cells in the presence of big ET-1, resulting in cell cont raction and desensitization to further ET-1 stimulation; in situ hybridizat ion analysis shows regional differences in ECE expression, suggesting that pulsatile production of endothelin by Sertoli cells (at specific "stages" o f the seminiferous epithelium) may regulate the cyclicity of tubular contra ction; when viewed in a scanning electron microscope, segments of seminifer ous tubules containing the specific stages characterized by high expression of ECE were observed to contract in response to big ET-1, whereas stages w ith low ECE expression remained virtually unaffected. These data indicate t hat endothelin-mediated spatiotemporal control of rhythmic tubular contract ility might be operated by Sertoli cells through the cyclic expression of E CE-1, which is, in turn, dependent upon the timing of spermatogenesis.