Participation of the Cl−/HCO3− Exchangers SLC26A3 and SLC26A6, the Cl− Channel CFTR, and the Regulatory Factor SLC9A3R1 in Mouse Sperm Capacitation1

Abstract

Sperm capacitation is required for fertilization and involves several ion permeability changes. Although Cl(-) and HCO(3)(-) are essential for capacitation, the molecular entities responsible for their transport are not fully known. During mouse sperm capacitation, the intracellular concentration of Cl(-) ([Cl(-)](i)) increases and membrane potential (Em) hyperpolarizes. As in noncapacitated sperm, the Cl(-) equilibrium potential appears to be close to the cell resting Em, opening of Cl(-) channels could not support the [Cl(-)](i) increase observed during capacitation. Alternatively, the [Cl(-)](i) increase might be mediated by anion exchangers. Among them, SLC26A3 and SLC26A6 are good candidates, since, in several cell types, they increase [Cl(-)](i) and interact with cystic fibrosis transmembrane conductance regulator (CFTR), a Cl(-) channel present in mouse and human sperm. This interaction is known to be mediated and probably regulated by the Na(+)/H(+) regulatory factor-1 (official symbol, SLC9A3R1). Our RT-PCR, immunocytochemistry, Western blot, and immunoprecipitation data indicate that SLC26A3, SLC26A6, and SLC9A3R1 are expressed in mouse sperm, localize to the midpiece, and interact between each other and with CFTR. Moreover, we present evidence indicating that CFTR and SLC26A3 are involved in the [Cl(-)](i) increase induced by db-cAMP in noncapacitated sperm. Furthermore, we found that inhibitors of SLC26A3 (Tenidap and 5099) interfere with the Em changes that accompany capacitation. Together, these findings indicate that a CFTR/SLC26A3 functional interaction is important for mouse sperm capacitation.

CFTR/ENaC-dependent regulation of membrane potential during human sperm capacitation is initiated by bicarbonate uptake through NBC

“…In addition to stimulating ADCY10, the uptake of HCO 3 -mice, it is postulated that a Na + -dependent electrogenic HCO 3 -incorporation through members of the Na + /HCO 3 cotransporter (NBC) is responsible for the initial anion entrance (11). It is also claimed that in mice the Cystic Fibrosis Transmembrane Conductance Regulator Channel (CFTR) works in association with other Cl -/HCO 3 -cotransporters to provide a sustained uptake of HCO 3 - (13,14). On the other hand, the mechanism of HCO 3 -entrance in human sperm is completely unknown.…”

Cl− Channels and Transporters in Sperm Physiology

“…Recent Western blot and immunofl uorescence results from several laboratories, including ours, indicate the presence of SLC26A3 and SLC26A6 in the sperm midpiece Chavez et al 2011 ;Chen et al 2009 ). Chavez et al ( 2011 ), also provided evidence that these transporters co-precipitate with CFTR and that tenidap, a specifi c SLC26A3 inhibitor, blocked the capacitation-associated hyperpolarization and the ZP-induced AR.…”

“…Chavez et al ( 2011 ), also provided evidence that these transporters co-precipitate with CFTR and that tenidap, a specifi c SLC26A3 inhibitor, blocked the capacitation-associated hyperpolarization and the ZP-induced AR. However, tenidap did not affect the activation of a cAMP pathway or the increase in tyrosine phosphorylation, suggesting that these transporters are not directly involved in the regulation of the soluble adenylate cyclase.…”

Sperm Capacitation and Acrosome Reaction in Mammalian Sperm

“…Sodium replacement from the external media by the non-permeant cation choline does not allow the hyperpolarization induced by HCO 3 À addition (Demarco et al 2003), suggesting the presence of an electrogenic Na + /HCO 3 À cotransporter in spermatozoa. Alternatively, it has also been proposed the presence of a neutral Na + /Cl À /HCO 3 À cotransporter (Zeng et al 1996) and the transport through CFTR (Chavez et al 2012) or its coupled Cl À /HCO 3 À exchangers (Chen et al 2009). Equilibrium of HCO 3 À /CO 2 is modulated by the presence of sperm carbonic anhydrases, which catalyze the reversible hydration of CO 2 to HCO 3 À .…”