Enzymes of adenosine metabolism in mouse sperm suspensions

Abstract

Summary. The enzymes of adenosine metabolism were investigated in suspensions of epididymal mouse spermatozoa incubated under conditions which support capacitation in vitro. High levels of adenosine deaminase activity were found in sperm suspensions, but the enzyme was located in the surrounding medium and was not intrinsic to spermatozoa. 5\m='\-Nucleotidase was also present in the surrounding medium while in sperm cells it existed as an ecto-enzyme. Adenosine was not metabolized by washed spermatozoa under conditions used for the assay of adenosine deaminase or adenosine kinase, but it was metabolized rapidly by unwashed sperm suspensions. Incubation of sperm suspensions in conditions which modulate fertilizing ability resulted in small alterations in intrinsic 5\m='\-nucleotidase activity of spermatozoa. In contrast, the activity of adenosine deaminase was not consistently modulated by such maniupulations.Adenosine deaminase and 5\m='\-nucleotidase exhibited similar kinetic parameters to enzymes from other sources and their activities were inhibited by coformycin and \ g = a \ , \ g = b \ \ x = r e q -\ methylene adenosine 5\m='\-diphosphate, respectively. These studies highlight the low adenosine-metabolizing ability of spermatozoa coupled with the extensive metabolism in the medium which surrounds them. Extracellular adenosine metabolism can therefore occur and may modulate capacitation in vitro.

High expression and activity of ecto-5′-nucleotidase/CD73 in the male murine reproductive tract

“…Immunolabelling and histochemical data reported here support the hypothesis that ecto-5 0 -nucleotidase is the main enzyme responsible for the accumulation of adenosine in sperm fluid, which would be of importance for epididymal function in sperm maturation and maintenance of fluid composition. Previous reports have demonstrated the presence of 5 0 -nucleotidase activity in mouse sperm suspensions (Monks and Fraser 1988). We have not detected ecto-5 0 -nucleotidase immunoreactivity in spermatozoa either isolated from cauda epididymides or in tissue slices.…”

“…AMP, the final product of NTPDases' activity might then be hydrolysed to adenosine by ecto-5 0 -nucleotidase (CD73), a glycosyl phosphatidylinositol (GPI)-linked membrane-bound glycoprotein (Colgan et al 2006;Resta et al 1993). Previous studies have pointed to the existence of 5 0 -nucleotidase activity in mouse sperm suspensions (Monks and Fraser 1988) although its expression along the male murine reproductive tract has not been studied so far.…”

Ecto-nucleotidases distribution in human cyclic and postmenopausic endometrium

“…Besides a function in the regulation of uterine fluid composition, a role for this enzyme in the generation of extracellular adenosine needed for sperm capacitation has been postulated [39][40][41]. We show here that in human endometrium ecto-5′-nucleotidase is expressed in glands, with more intensity in the basal layer, and in the stroma, but not in luminal epithelium.…”

Na+ Reabsorption in Cultured Rat Epididymal Epithelium via the Na+/Nucleoside Cotransporter1

“…Thus, the Na ϩ /H ϩ exchanger should be a major candidate involved in Na ϩ and fluid reabsorption by the epididymis. It is conceivable that a high concentration of nucleosides exists in the epididymal fluid, and they could be derived from the hydrolysis of nucleotides by 5Ј-ectonucleotidase, which has been found on the plasma membranes of spermatozoa [23][24][25] and epididymal epithelial cells [26]. This study shows that the Na ϩ /nucleoside cotransporter may also contribute to Na ϩ and fluid reabsorption across the epididymal tubules.…”