The article summarizes and analyzes published material related to the functioning and properties of passive ion-transporting systems in mammalian, in particular human spermatozoa. Transporting systems of K+, H+, Cl–, Ca2+ and their impact on sperm functional status and mammals fertility were described. Close attention was given to iontransporting systems, the presence of which is proved in human spermatozoa.

Spermatogenic cells and sperm have been reported to possess Ca2+-activated K+-channels, voltage-gated K+-channels, two-pore domain K+ channels, inwardly rectifying K+ (Kir) channels and Slo3 K+ channels.

The potassium voltage-gated channel Ksper (Slo3) expressed only in spermatogenic cells and sperm, has only recently been shown to be fundamental for sperm function. IKSper is the only detectable hyperpolarizing current in spermatozoa and largely sets its resting membrane potential. It is suggested that IKSper is encoded by Slo3 on the basis of its tissue localization and other properties. Slo3−/− mice are infertile and do not exhibit capacitation-dependent membrane hyperpolarization. Incapacitated Slo3−/− sperm also have modest defects in motility. Only 10% of Slo3−/− sperm were able to fertilize oocytes during in vitro fertilization experiments. Slo3 channel activation is pivotal for the capacitation-associated processes necessary for fertilization.

It is feasible that K+ inwardly rectifying channels Kir such as the KATP channels contribute to the capacitation-associated hyperpolarization in mammalian sperm. Recent evidence has revealed that mammalian sperm, particularly those of human, express HV channels. A voltage-gated proton channel Hv1 (HVCN1) appears to play an important role in the regulation of human sperm pHi.

Another possible role assigned to Hv1 is the regulation of intracellular Ca2+ homeostasis. By functioning so, it can potentially influence almost every aspect of sperm behavior in the female reproductive tract, including initiation of motility, capacitation, hyperactivation, and the acrosome reaction. Cyclic nucleotide-gated (CNG) channels have also been proposed as mediating sperm Ca2+ influx. CNG channels may be responsible for the cyclic nucleotide-induced Ca2+ influx in sperm. A more recent variation of this model proposes that cyclic nucleotides activate the hyperpolarization-activated and cyclic nucleotide–gated (HCN) channels, resulting in the depolarization and subsequent opening of Ca2+ channels.

Several of the 28 members of the transient receptor potential (TRP) ion channels were recently proposed to function in mature spermatozoa. Particularly, TRPC channels may act as candidate molecular entities for storeoperated channels that are responsible for the sustained Ca2+ elevations necessary for normal physiologic function. Some of TRPC channels, that are functionally important in sperm activation, have been expressed in mammalian sperm. Few studies have reported the presence of a thermosensitive channel TRPM8 in human sperm. This channel might have a role in cellular signaling (i.e. thermotaxis and chemotaxis mechanism involved in guiding the sperm during fertilization).

CFTR – cAMP-modulated, ATP-dependent Cl– channel have been detected in the midpiece of mouse and human sperm flagella.

Other channels, that regulate the membrane potential and intracellular ionic concentration and thus serve a central role in various cellular processes in spermatozoa, have also been mentioned.

Keywords: spermatozoa, ion transport, ion channels, potassium

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