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Intracellular calcium and protein tyrosine phosphorylation during the release of bovine sperm adhering to the fallopian tube epithelium in vitro

Dipartimento di Biologia Evolutiva e Comparata, Università di Napoli ‘Federico II’, Via Mezzocannone 8, 80134 Napoli, Italy, ¹ Dipartimento di Scienze delle Produzioni Animali, Campus Macchia Romana, 85100 Potenza, Italy and ² Stazione Zoologica ‘Anton Dohrn’, Villa Comunale, Napoli, Italy

Correspondence should be addressed to R Gualtieri; Email: roberto.gualtieri{at}unina.it

In mammals, sperm adhesion to the epithelial cells lining the oviductal isthmus plays a key role in the maintenance of motility and in the selection of superior quality subpopulations. In the bovine species, heparin and other sulfated glycoconjugates powerfully induce the synchronous release of sperm adhering to tubal epithelium in vitro and may represent the signal which triggers release at ovulation in vivo. Sperm detachment may be due either to surface remodeling or to hyperactivation brought about by capacitation. In this paper, the dynamics of intracellular free Ca²⁺concentration ([Ca²⁺]_i) and protein tyrosine phosphorylation in sperm during and after heparin-induced release from in vitro cultured oviductal monolayers were assessed to determine whether this event is due to capacitation. Moreover, Ca²⁺-ionophore A23187, thapsigargin, thimerosal and caffeine were used to determine whether [Ca²⁺]_i increase and/or hyperactivation can induce sperm release. Results showed that: 1. heparin-released sperm have significantly higher [Ca²⁺]_i than adhering sperm; 2. heparin induces a [Ca²⁺]_i elevation in the sperm head followed by detachment from the monolayers; 3. external Ca²⁺is not required for heparin-induced release; 4. [Ca²⁺]_i increase and/or hyperactivation are unable to release sperm; and 5. heparin-released sperm have an increased level of tyrosine phosphorylated proteins compared with adhering sperm. In conclusion, although heparin is considered a long-lasting capacitation agent, it quickly modulates the capacitation of bovine sperm adhering to the fallopian epithelium, probably leading to surface remodeling and therefore to the release of sperm selected and stored within the oviduct through adhesion.

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