Rat testicular myoid cells respond to endothelin: characterization of binding and signal transduction pathway.
The presence of endothelin (ET), a vasoconstrictor peptide, in the testis suggests that it may regulate nonvascular target cells. We investigated binding ability, regulation of inositol phosphate metabolism, changes in cytosolic free Ca2+ concentrations ([Ca2+]i), and induction of morphological changes by ET-1 in rat primary testicular myoid cell cultures. ET-1 specifically bound to highly purified rat testicular myoid cells in a time- and temperature-dependent manner. Scatchard analysis of the binding studies indicated the presence of a single class of high affinity binding sites, with an apparent Kd of 3 x 10(-10) M and a maximal binding capacity of 10(5) sites/cell. ET-1 induced both rapid production of inositol triphosphate and mobilization of [Ca2+]i in a concentration-dependent fashion. By contrast, inositol lipid metabolism was slightly affected by ET-1 in the total peritubular cell population. Purified Sertoli cells failed to show either ET-1 binding or ET-1-induced phosphatidylinositol hydrolysis. Mobilization of [Ca2+]i mostly depended upon the release of Ca2+ from thapsigargin-sensitive intracellular Ca2+, whereas it was not affected by abolishment of the Ca2+ gradient through the plasma membrane or by inhibition of L-type voltage-sensitive Ca(2+)-channels by nifedipine. These findings together with the fact that Sertoli cells are unable to respond to and bind ET-1 indicate that ET is a specific agonist of myoid cells in the seminiferous tubule and suggest a role for ET-1 in the autocrine/paracrine regulation of testicular function.
Filippini
A
A
Institute of Histology and General Embryology, La Sapienza, University of Rome School of Medicine, Italy.
Tripiciano
A
A
Palombi
F
F
Teti
A
A
Paniccia
R
R
Stefanini
M
M
Ziparo
E
E
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D016232:Endothelins / Q000378:metabolism* / Q000494:pharmacology*; D007295:Inositol Phosphates / Q000096:biosynthesis; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D009994:Osmolar Concentration; D051381:Rats; D015398:Signal Transduction; D013737:Testis / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*
D016232:Endothelins; D007295:Inositol Phosphates; D002118:Calcium