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Cl^– Is Required for HCO₃^– Entry Necessary for Sperm Capacitation in Guinea Pig: Involvement of a Cl^–/HCO₃^– Exchanger (SLC26A3) and CFTR¹

Unit of Reproductive Physiology,⁴ Institute of Reproductive Health, Zhejiang Academy of Medical Sciences, Hangzhou 310013, China Department of Physiology,⁵ Faculty of Medicine, Epithelial Cell Biology Research Center, Li Ka Shing Institute of Health Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong Experimental Animal Center of Zhejiang Province,⁶ Hangzhou 310013, China Hospital for Children and Adolescents,⁷ Department of Medical Genetics, University of Helsinki, FI-00014 Helsinki, Finland

ABSTRACT

Our previous study demonstrated the involvement of cystic fibrosis transmembrane conductance regulator (CFTR) in transporting bicarbonate that is necessary for sperm capacitation; however, whether its involvement is direct or indirect remains unclear. The present study investigated the possibility of a Cl^–/HCO₃^– exchanger (solute carrier family 26, number 3 [SLC26A3]) operating with CFTR during guinea pig sperm capacitation. Incubating sperm in media with various concentrations of Cl^– resulted in varied percentages of capacitated sperm in a concentration-dependent manner. Depletion of Cl^–, even in the presence of HCO₃^–, abolished sperm capacitation and vice versa, indicating the involvement of both anions in the process. Capacitation-associated HCO₃^–-dependent events, including increased intracellular pH, cAMP production, and protein tyrosine phosphorylation, also depend on Cl^– concentrations. Similar Cl^– dependence and inhibitor sensitivity were observed for sperm-hyperactivated motility and for sperm-egg fusion. The expression and localization of CFTR and SLC26A3 were demonstrated using immunostaining and Western blot analysis. Taken together, our results indicate that Cl^– is required for the entry of HCO₃^– that is necessary for sperm capacitation, implicating the involvement of SLC26A3 in transporting HCO₃^–, with CFTR providing the recycling pathway for Cl^–.

bicarbonate, CFTR, chloride, SLC26A3, sperm capacitation

¹Supported by grant 2006CB504002 from the National "973" Project of China, by grants 30270513 and 30600217 from the National Science Foundation of China, by grant CUHK4534/05M from the Li Ka Shing Institute of Health Sciences of The Chinese University of Hong Kong and the Research Grants Council of Hong Kong, by grant WKJ 2005204701 from the Ministry of Public Health of China, and by grant 2006B002 from the Zhejiang Province Medical Science Research Fund. H.C.C. received the Croucher Senior Research Fellowship for 2007–2008.

Correspondence: ²FAX: 852 26035022; e-mail: hsiaocchan{at}cuhk.edu.hk

Correspondence: ³FAX: 86 571 8807 5447; e-mail: qx_shi{at}126.com