Electrophysiological evidence for the presence of cystic fibrosis transmembrane conductance regulator (CFTR) in mouse sperm

Abstract

Mammalian sperm must undergo a maturational process, named capacitation, in the female reproductive tract to fertilize the egg. Sperm capacitation is regulated by a cAMP/PKA pathway and involves increases in intracellular Ca2+, pH, Cl−, protein tyrosine phosphorylation, and in mouse and some other mammals a membrane potential hyperpolarization. The cystic fibrosis transmembrane conductance regulator (CFTR), a Cl− channel modulated by cAMP/PKA and ATP, was detected in mammalian sperm and proposed to modulate capacitation. Our whole-cell patch-clamp recordings from testicular mouse sperm now reveal a Cl− selective component to membrane current that is ATP-dependent, stimulated by cAMP, cGMP and genistein (a CFTR agonist, at low concentrations), and inhibited by DPC and CFTRinh-172, two well-known CFTR antagonists. Furthermore, the Cl− current component activated by cAMP and inhibited by CFTRinh-172 is absent in recordings on testicular sperm from mice possessing the CFTR ΔF508 loss-of-function mutation, indicating that CFTR is responsible for this component. A Cl− selective like current component displaying CFTR characteristics was also found in wild type epididymal sperm bearing the cytoplasmatic droplet. Capacitated sperm treated with CFTRinh-172 undergo a shape change, suggesting that CFTR is involved in cell volume regulation. These findings indicate that functional CFTR channels are present in mouse sperm and their biophysical properties are consistent with their proposed participation in capacitation.

Flow Cytometry Analysis Reveals That Only a Subpopulation of Mouse Sperm Undergoes Hyperpolarization During Capacitation1

“…Among the most likely possibilities, changes towards a more negative Em during sperm capacitation can be explained by: 1) the opening of K þ channels, such as SLO3 [21,29,30] or other inward rectifiers [20,31] or 2) the closing of Na þ channels, such as the amiloride-sensitive epithelial Na þ channels (ENaCs; [18,32]) mediated by activation of the cystic fibrosis transmembrane regulator (CFTR; [32][33][34][35]). Favoring the first hypothesis is the observation that sperm from Slo3-null mice do not undergo the capacitation-associated hyperpolarization [31,33,36,37].…”

Intracellular pH in sperm physiology

“…The second group is constituted by the HCO 3 − transporters of the SLC4 [14], [15], SLC26 families [16]. and the cystic fibrosis transmembrane conductance regulator (CFTR) is able to conduct HCO 3 − [17]–[21]. As carbonic anhydrases (CAs) catalyze CO2/HCO3- equilibrium, they are also considered.…”

Cl− Channels and Transporters in Sperm Physiology

“…NFA also partially inhibited a Ca 2+ -induced hyperpolarization partially driven by Cl − in mouse spermatozoa (Espinosa et al 1998 ). Anion channel blockers such as NFA, for example, DIDS, also inhibit the mouse and human sperm AR, as well as Cl − channels detected in these cells (Espinosa and Darszon 1995 ;Espinosa et al 1998 ;Figueiras-Fierro et al 2013 ;Orta et al 2012 ).…”

“…In spermatozoa, as in other cells, Cl − is the main anion and is involved in volume regulation and osmotic stress protection (Cooper and Yeung 2007 ;Furst et al 2002 ;Yeung et al 2005 ). Capacitation, a maturational process and the AR, a unique exocytotic event essential for fertilization, both discussed next, are signifi cantly affected in mouse and human spermatozoa when external Cl − concentrations are lowered Figueiras-Fierro et al 2013 ;Orta et al 2012 ;Wertheimer et al 2008 ;Yeung and Cooper 2008 ). Although these fi ndings suggest that Cl − plays a relevant role in sperm physiology, not much is known about its transport across the membrane of this fundamental cell.…”