Estradiol inhibits the effects of extracellular ATP in human sperm by a non genomic mechanism of action

Abstract

Steroid hormones, beside their classical genomic mechanism of action, exert rapid, non genomic effects in different cell types. These effects are mediated by still poorly characterized plasma membrane receptors that appear to be distinct from the classic intracellular receptors. In the present study we evaluated the non genomic effects of estradiol (17bE 2 ) in human sperm and its effects on sperm stimulation by extracellular ATP, a potent activator of sperm acrosome reaction. In human sperm 17bE 2 induced a rapid increase of intracellular calcium (Ca 2+ ) concentrations dependent on an influx of Ca 2+ from the extracellular medium. The monitoring of the plasma membrane potential variations induced by 17bE 2 showed that this steroid induces a rapid plasma membrane hyperpolarization that was dependent on the presence of Ca 2+ in the extracellular medium since it was absent in Ca 2+ free-medium. When sperm were pre-incubated in the presence of the K + channel inhibitor tetra-ethylammonium, the 17bE 2 induced plasma membrane hyperpolarization was blunted suggesting the involvement of K + channels in the hyperpolarizing effects of 17bE 2 . Extracellular ATP induced a rapid plasma membrane depolarization followed by acrosome reaction. Sperm preincubation with 17bE 2 inhibited the effects of extracellular ATP on sperm plasma membrane potential variations and acrosome reaction. The effects of 17bE 2 were specific since its inactive steroisomer 17aE 2 was inactive. Furthermore the effects of 17bE 2 were not inhibited by tamoxifen, an antagonist of the classic 17bE 2 intracellular receptor.

Involvement of a P2X7 Receptor in the Acrosome Reaction Induced by ATP in Rat Spermatozoa

“…In this work, we proposed the participation of P2X7 receptors in the AR induced by ATP of rat spermatozoa based on: (1) the AR induced by ATP is prevented by general P2 receptor inhibitors such as Suramin and oATP; (2) BzATP is 500 times more potent than ATP to induce AR; (3) the AR is prevented by 17−β‐oestradiol and BB‐G, two blockers of P2X7 ion currents in other cell types; (4) it is present in the mature spermatozoa and localized in the tail and in the acrosomal domain of the head. Our results agree with previous reports in human spermatozoa that 17‐β‐oestradiol prevents the AR induced by ATP (Foresta et al, ; Rossato et al, ). On the other hand, a previous study showed a bivalent ion current evoked by ATP in epidydimal non‐capacitated mouse spermatozoa (Navarro et al, ).…”

“…It has also been shown that 3 μM 17β‐oestradiol inhibits the P2X7 receptor cation current by a non‐genomic pathway and that it prevents the AR induced by ATP in human spermatozoa (Cario‐Toumaniantz et al, ; Rossato et al, ) We observed that in rat spermatozoa, 3 μM 17β‐oestradiol significantly prevented the AR in capacitated rat spermatozoa incubated with 1 μM BzATP or 500 μM ATP (Fig. C and D).…”

“…and that it prevents the AR induced by ATP in human spermatozoa (Cario-Toumaniantz et al, 1998;Rossato et al, 2005) We observed that in rat spermatozoa, 3 mM 17b-oestradiol significantly prevented the AR in capacitated rat spermatozoa incubated with 1 mM BzATP or 500 mM ATP ( Fig. 3C and D).…”

Calcium Channels in the Development, Maturation, and Function of Spermatozoa

“…Other cellular ligands can induce the AR such as progesterone (31, 55, 355, 506), ␥-aminobutyric acid (GABA) (280,355,559), glycine (301), EGF (133), ATP (339,442), acetylcholine (66), and sphingosine-1-phosphate (495). The role of many of these "alternative" agonists is not clear.…”

Purinergic signalling in the reproductive system in health and disease

“…Nevertheless, fertility of male P2X2 knockout mice declined with frequent mating over days, suggesting that P2X2 receptors add a selective advantage under these conditions. Sperm preincubation with oestradiol 17βE 2 inhibited the effects of extracellular ATP on sperm plasma membrane potential variations and the acrosome reaction [352]. Extracellular ATP improves human sperm motility parameters and provides a rational explanation for increased IVF percentages when sperm is treated with ATP [103].…”