Reproduction Abstracts

CatSper channels are expressed specifically in the principal piece of the sperm flagellum. In human sperm Catsper channel activation is polymodal and sensitive to increased pHi, progesterone and other agonists, potentially resulting in synergistic enhancement of Ca²⁺ influx and hyperactivation (1) We have investigated if the interaction of pHi with the CatSper agonist progesterone and 4-aminopyridine (4AP), a potent activator of hyperactivation in human sperm. [Ca²⁺]_i, pHi and motility were monitored using a fluorescent plate reader and CEROS CASA system. Incubation of capacitated human sperm at pH values between 6.0 and 9.0 resulted in proportional changes in pHi. At pHo=7.4 (pHi=6.9) and pHo=8.5 (pHi=7.2) the % hyperactivated cells was 2.50.7 and 12.31.8respectively (n=21, P=2×10⁻⁶). Treatment with progesterone (0.1–20 μM) to stimulate CatSper channels induced only a modest increase in hyperactivation that was similar at pHo=7.4 and pHo=8.5. The amplitude of this effect was inversely proportional to the spontaneous level of hyperactivation. In contrast, effect of 4-AP (0.2–5 mM) on hyperactivation was significantly greater than progesterone and was stronger and more potent at pHo=8.5 than at pHo=7.4. Resting [Ca²⁺]_i was higher in cells incubated at pHo=8.5 than at pHo=7.4. Both progesterone (0.001–20 μM) and 4-AP (0.2–5 mM) induced dose-dependent elevation of [Ca²⁺]_i but at pHo=8.5 the effect of 4-AP was greater than at pHo=7.4. These data show that: i) Catsper activation by progesterone only weakly enhances hyperactivation of human sperm and though alkalinisation increases [Ca²⁺]_i this treatment does not interact synergistically with progesterone to enhance hyperactivation; ii) the more potent effect of 4-AP on hyperactivation is significantly enhanced at high pHi, suggesting that the action of 4-AP on human sperm [Ca²⁺]_i/hyperactivation involves a different pathway.

Reference

1. Alasmari et al. J. Biol. Chem. 2013 288 (9), 6248–6258.