Follicle-stimulating hormone-dependent estrogen secretion by rat Sertoli cells in vitro: modulation by calcium

Extracellular ATP stimulates estradiol secretion in rat Sertoli cells in vitro: modulation by external sodium

In this study, we examined the effects of extracellular ATP (ATPe) on [Ca(2+)](i), [Na(+)](i), plasma membrane potential changes and estradiol secretion in rat Sertoli cells. ATPe caused a rapid rise of [Ca(2+)](i) with an initial spike followed by a long lasting plateau. The first rapid spike was dependent on the release of Ca(2+) from internal stores as it also occurred in Ca(2+)-free medium while the long lasting plateau phase was dependent on Ca(2+) influx from the external medium. ATPe stimulated a rapid plasma membrane depolarization that was dependent on an influx of Na(+) from the external medium as demonstrated by plasma membrane potential monitoring in Na(+)-free medium and by [Na(+)](i) measurement with the Na(+)-sensitive fluorescent dye SBFI. ATPe stimulated estradiol secretion in a dose dependent manner and was fully dependent on the presence of Na(+) in the external medium while the presence of Ca(2+) was not necessary. Among the different nucleotides tested, only ATP, ATP-5'-[gamma-thio]triphosphate, UTP, alpha,beta-methylene-ATP were effective in stimulating estradiol secretion. These results demonstrate that rat Sertoli cells possess P2-purinergic receptors belonging to the P2X and P2Y subfamily which activation induces [Ca(2+)](i) and [Na(+)](i) rise and Na(+)-dependent plasma membrane depolarization leading to estradiol secretion.

Regulation of Sertoli cell aromatase activity by cell density and prolonged stimulation with FSH, EGF, insulin and IGF-I at different moments of pubertal development

Sertoli cell aromatase activity is high in very young animals and declines throughout pubertal development. Little is known about the regulatory factors which might be involved in the pronounced decline suffered by this enzymatic activity. In this paper we show that estradiol production in Sertoli cells is dependent on cell density in the culture and that chronic stimulation with hormones can decrease estradiol acute response to FSH. In 8-day-old Sertoli cells cultured at low density (LD: 7.1 +/- 0.3 micrograms DNA), estradiol production was 151 +/- 11 pgE2/micrograms DNA, while in those cultured at high density (HD: 30.3 +/- 0.6 micrograms DNA), production was 30 +/- 5 pgE2/micrograms DNA. Similar results were obtained in 20-day-old Sertoli cell cultures (LD: 57 +/- 4 pgE2/micrograms DNA vs HD: 26.0 +/- 0.6 pgE2/micrograms DNA). On the other hand, treatment of Sertoli cell cultures (8- and 20-day-old) for 96 h, with FSH (100 ng/ml), EGF (50 ng/ml), insulin (10 micrograms/ml) and IGF-I (50 ng/ml) at different densities resulted mostly in inhibition of aromatase activity. The effect caused by FSH was apparently not related to desensitization as aromatization with dbcAMP could not overcome the decreased ability of these cells to produce estradiol. The effect caused by EGF was observed in 8-day-old Sertoli cells cultured under high density conditions. Marked inhibition was observed with insulin and IGF-I in 8-day-old Sertoli cell cultures. Considering previous reports indicating a decrease in Sertoli cell aromatase activity with age, our results suggest a potential role for FSH, EGF, insulin and IGF-I on the Sertoli cell differentiation process which occurs throughout pubertal development.

The comparative cell biology of accessory somatic (or Sertoli) cells in the animal testis

A comparative account is given of recent advances in the cell biology of testicular accessory somatic (or Sertoli) cells in mammals, nonmammalian vertebrates, and invertebrates by comparing and contrasting their structure and function. Their structure is discussed in relation to the nucleus, cytoplasmic organelles, and inclusions (lipids, the cytoskeleton, junctional complexes, and blood-testis barrier, which show great diversity and a variable testicular architecture), and mode of spermatogenesis. A very limited somatic cell-germinal association or its complete absence is observed in some groups of invertebrates. Wherever the somatic accessory cells are present, their comparative functions are discussed in relation to (1) mechanical support and nutrition; (2) translocation of germ cells; (3) paracrine regulation and a combination of male germ cell proliferation and differentiation by secretion of regulatory proteins, including peptide growth factors and hormones; (4) phagocytosis; (5) steroid hormone synthesis and metabolism; and (6) spermiation. Comparative cellular and molecular aspects of Sertoli cell-germ cell and peritubular cell interactions and the regulatory (hormonal) mechanisms involved as well as gaps in our knowledge about the molecular aspects of these interactions are emphasized for a better understanding of diversity in the patterns and regulation of spermatogenesis in animals.

A tetrapeptide within a receptor-binding region of human follicle-stimulating hormone beta-subunit, hFSH-beta-(34-37), regulates sodium-calcium exchange in Sertoli cells

In a previous study, we showed that binding of FSH by cultured rat Sertoli cells significantly inhibited basal levels of Na+/Ca2+ exchange. Similar inhibition was observed when proteoliposomes enriched with bovine calf testis follicle-stimulating hormone (FSH) receptors were stimulated with FSH. In the present study, we screened a series of overlapping synthetic peptide amides, representing the entire primary structure of the beta-subunit of hFSH, for their effects on sodium-dependent calcium uptake (as 45Ca2+) by monolayer cultures of Sertoli cells from immature rats. hFSH-beta-(33-53), previously identified as a receptor binding region of hFSH-beta-subunit, significantly (P < 0.05) inhibited Na+/Ca2+ exchange. A tetrapeptide [TRDL, hFSH-beta-(34-37)] contained within this sequence, was observed to be equally as active as hFSH-beta-(33-53) at 200 microM, suggesting that the regulatory effect of hFSH-beta-(33-53) on sodium-dependent 45Ca2+ influx was due to residues 34-37. hFSH-beta-(81-95) also inhibited Na(+)-dependent calcium influx, although to a lesser extent than hFSH-beta-(33-53) or hFSH-beta-(34-37). Sodium-dependent 45Ca2+ entry into Sertoli cells was enhanced in a concentration-related manner when extracellular sodium was replaced by equimolar concentrations (up to 135 mM) of choline chloride. hFSH-beta-(34-37) significantly reduced basal uptake of 45Ca2+ in choline-containing buffer, but was without effect in buffer containing 135 mM NaCl.(ABSTRACT TRUNCATED AT 250 WORDS)