REPLACEMENT OF CALCIUM FOR STRONTIUM IN HAMSTER SPERM INCUBATION MEDIA: EFFECT ON SPERM FUNCTION.

BACHMANN S; MENÉNDEZ HELMAN RJ; ZITTA K; WERTHEIMER EV; MIRANDA PV.

MOLECULAR HUMAN REPRODUCTION.

OXFORD UNIV PRESS

Lugar: Childerley, Cambs. UK.; Año: 2012 vol. 18 p. 22 - 32

1360-9947

Calcium (Ca2+) is an absolute requirement for a decisive sperm function event: the acrosome reaction (AR). Physiologically, sperm capacitation is a prerequisite for this specialized exocytosis and both events are intimately related. In an effort to separate capacitation from AR, we have been using a modified sperm incubation medium where Ca2+ is replaced by Strontium (Sr2+). The aim of this report is to analyze with more detail the difference between sperm incubated with Ca2+ or Sr2+ in several events. We found that sperm undergo the capacitation-related changes in the chlortetracycline (CTC) pattern and tyrosine phosphorylation, and also bind to the zona pellucida (ZP) when using Sr2+-instead of Ca2+-containing media. However, the spontaneous AR typical of hamster sperm does not take place in Sr2+-medium, even if sperm are previously capacitated with Ca2+. Nevertheless, Sr2+ was able to sustain AR when cells were treated with thapsigargin or depolarized with K+ in Na+-depleted medium. Considering that the absence of Na+ increased spontaneous AR in Sr2+-medium, we tested whether Na+-transport systems could be involved in the inability of Sr2+-incubated sperm to undergo AR. We found that when sperm incubated in Sr2+-medium are treated with amiloride to inhibit epithelial Na+ channel (ENaC), they are able to undergo spontaneous AR. The same result was obtained when analyzing AR on the ZP. On the contrary, addition of ouabain (a Na+/K+-ATPase inhibitor) or DIDS (a Na+/HCO3− co-transporter inhibitor) showed no effect. These results suggest that, differing from what happens in Ca2+-incubated sperm, cells incubated in Sr2+-modified medium would have an active ENaC.