Molecular basis of bicarbonate membrane transport in the male reproductive tract.

Bicarbonate (HCO₃⁻) membrane transport systems are crucial players in the physiology of several tissues. The molecular basis of HCO₃⁻ membrane transport is of major physiological relevance since this ion is involved in the establishment of intracellular and extracellular ionic composition, osmolariy and pH. The membrane HCO₃⁻ transporters are divided in two main families: solute carrier 4 (SLC4) and solute carrier 26 (SLC26), although HCO₃⁻ concentration can also be regulated by the cystic fibrosis transmembrane regulator (CFTR). In most tissues the SLC4 family represents the majority of HCO₃⁻ transporters members, which can be divided in two subgroups: the Na⁺-dependent and the Na⁺-independent transporters. The SLC26 family consists of ten members that can transport diverse ions besides HCO₃⁻. In the male reproductive tract, HCO₃⁻ transport occurs in several processes in order to assure a correct pursuance of the spermatogenetic event and spermatozoa capacitation, being also necessary for egg fertilization. Indeed, the formation of competent spermatozoa, the maintenance of an adequate ductal luminal milieu and spermatozoa capacitation are highly dependent of ionic balance and pH. Perturbations in these processes result in reduced male reproductive health and consequently male subfertility and/or infertility. Thus, it is imperative to understand HCO₃⁻ transport dynamics in order to identify and counteract possible alterations related with reduced male fertility caused by pathological conditions. Herein, we will review the major families and subfamilies of HCO₃⁻ membrane transport, discussing the molecular basis of HCO₃⁻ transport in the male reproductive tract and its role in male-associated subfertility and/or infertility.