Acute effects of adenosine triphosphates, cyclic 3',5'-adenosine monophosphates, and follicle-stimulating hormone on cytosolic calcium level in cultured immature rat sertoli cells

Abstract

The ability of ATP and FSH to induce intracellular calcium [Ca2+](i) changes in Sertoli cells is imperfectly understood and reports are conflicting. We have applied the single-cell microfluorometry technique with the calcium probe indo-1 to investigate [Ca2+](i) in individual cultured Sertoli cells. When cells were exposed to ATP, cAMP, and FSH, a fast and biphasic increase in [Ca2+](i) was obtained in 100%, 70%, and 56% of cells, respectively. Caffeine did not activate Ca2+ mobilization, while thapsigargin suppressed the peak response. External calcium free-EGTA buffer suppressed the plateau phase, while blockers of voltage-operated Ca2+ channels did not abolish the response to cAMP and ATP. We conclude that the three messengers mobilized Ca2+ from intracellular thapsigargin-sensitive stores, which induced a subsequent Ca2+ influx from the extracellular medium by a voltage-independent Ca2+ entry. The well-documented mechanisms by which these messengers act on cells support the idea that they release Ca2+ from smooth endoplasmic reticulum by two different pathways, or that FSH and cAMP first release ATP, which then acts on cells. Among the cells, 77% and 80% responded, respectively, to FSH and cAMP by a delayed long- lasting decrease in [Ca2+](i) that was never recorded in the presence of ATP. This suggests that FSH and cAMP also promote a slow redistribution of [Ca2+](i) from the exchangeable pool to the bound nonexchangeable pools. Involvement of voltage-operated and voltage-independent calcium channels in the response of Sertoli cells to ATP, FSH, and cAMP is discussed.