ATP-sensitive K⁺ (K_ATP) channels have been described in a variety of cell types. They exhibit the unique property to couple intracellular metabolic changes to membrane electrical activity. Closure of K_ATP channels results in membrane depolarization leading to the opening of voltage-dependent calcium channels and subsequent calcium entry. K_ATP channels consist of hetero-octameric complexes constituted by 4 pore-forming subunits (Kir6.x) and 4 regulatory sulfonylurea receptor subunits (SURx). K_ATP channels subunits have been described in mouse spermatogonia and spermatozoa. The study was designed to ascertain the presence of K_ATP channels in spermatozoa from various mammalian species and to investigate their potential role in modulating calcium influx.

Kir6.2, Kir6.1 and SUR2 subunits were detected on rat, mouse, dog, stallion and man spermatozoa. Western blot analysis confirmed the expression of Kir6.1 and Kir6.2 subunits in protein extracts from murine spermatozoa. mRNAs for Kir6.2, Kir6.1 and SUR2 subunit were detected by RT-PCR technique on mouse total RNA extracts. Cytosolic calcium measurements showed an increase in [Ca²⁺]_i in response to various hypoglycaemic sulfonylureas (glibenclamide, gliclazide, tolbutamide). The absence of extracellular calcium abolished this response. The addition of Ni²⁺ also counteracted the tolbutamide-induced [Ca²⁺]_i increase. Moreover, the tested sulfonylureas provoked a significant increase in the acrosome reaction of capacitated spermatozoa. This study reports the expression of K_ATP channel subunits on spermatozoa from various mammalian species. Our observations further suggest the existence of functional K_ATP channels involved in the control of spermatozoa membrane potential and, as a consequence, of calcium influx and acrosome reaction.