A Review on the Role of Bicarbonate and Proton Transporters during Sperm Capacitation in Mammals

Abstract

Alkalinization of sperm cytosol is essential for plasma membrane hyperpolarization, hyperactivation of motility, and acrosomal exocytosis during sperm capacitation in mammals. The plasma membrane of sperm cells contains different ion channels implicated in the increase of internal pH (pHi) by favoring either bicarbonate entrance or proton efflux. Bicarbonate transporters belong to the solute carrier families 4 (SLC4) and 26 (SLC26) and are currently grouped into Na+/HCO3− transporters and Cl−/HCO3− exchangers. Na+/HCO3− transporters are reported to be essential for the initial and fast entrance of HCO3− that triggers sperm capacitation, whereas Cl−/HCO3− exchangers are responsible for the sustained HCO3− entrance which orchestrates the sequence of changes associated with sperm capacitation. Proton efflux is required for the fast alkalinization of capacitated sperm cells and the activation of pH-dependent proteins; according to the species, this transport can be mediated by Na+/H+ exchangers (NHE) belonging to the SLC9 family and/or voltage-gated proton channels (HVCN1). Herein, we discuss the involvement of each of these channels in sperm capacitation and the acrosome reaction.

Human Sperm as an In Vitro Model to Assess the Efficacy of Antioxidant Supplements during Sperm Handling: A Narrative Review

“…One of the most important roles of ROS in sperm physiology (Figure 2) concerns the process of capacitation by which spermatozoa undergo dramatic changes in the membrane composition and acquire hyperactivated motility, leading to the acrosome reaction and fertilisation [53,54]. The molecular processes behind capacitation include an increase in pH, Ca 2+ and HCO 3 − influx, efflux of cholesterol from the plasma membrane, an increase in cyclic adenosine monophosphate (cAMP) concentration; and protein hyperphosphorylation [55,56]. During capacitation, the concentration of O 2…”

pH Homeodynamics and Male Fertility: A Coordinated Regulation of Acid-Based Balance during Sperm Journey to Fertilization

“…Notably, alkalinization of the intracellular pH (pH i ) of spermatozoa is required for sperm capacitation in mammals as well as for hyperactivation of sperm motility, chemotaxis, the acrosome reaction (AR), and fertilization [ 17 , 18 ]. HCO 3 − and H + transport are critical processes in pH i regulation [ 19 ]. pH homeostasis in the male reproductive tract is managed primarily by the transporters solute carrier 4 (SLC4) and solute carrier 26 (SLC26), Na + -H + exchangers (NHEs), carbonic anhydrases (CAs), monocarboxylate transporters (MCTs), and hydrogen voltage-gated channels (HVCN1), as well as by other channels and enzymes associated with pH regulation, including Ca 2+ channels (CatSper) [ 20 ], K + channels (SLO3) [ 21 ], and soluble adenylate cyclase (sAC) [ 22 ].…”

Signaling Roleplay between Ion Channels during Mammalian Sperm Capacitation

“…An increase in pH i and alkalization of sperm cytosol is essential for hyperpolarization of the plasmatic membrane and later hyperactivation of sperm motility via a Ca 2+ -dependent pathway. Membrane potential (Em) or resting membrane potential (Em r ) reflects different concentrations of ions (mmol/L) between intra- and extra-cellular spaces [ 1 , 2 , 3 ]. During capacitation, sperm cells change membrane potential by the process called hyperpolarization, which increases a negative charge of membrane through to reduced permeability for Na + and increased permeability for K + .…”