Carnitine/organic cation transporter OCTN2-mediated transport of carnitine in primary-cultured epididymal epithelial cells

Abstract

Carnitine is essential for the acquisition of motility and maturation of spermatozoa in the epididymis, and is accumulated in epididymal fluid. In this study, carnitine transport into primary-cultured rat epididymal epithelial cells was characterized to clarify the nature of the transporter molecules involved. Uptake of carnitine by primary-cultured epididymal epithelial cells was time, Na 1 and concentration dependent. Kinetic analysis of carnitine uptake by the cells revealed the involvement of high-and low-affinity transport systems with Km values of 21 mM and 2.2 mM respectively. The uptake of carnitine by the cells was significantly reduced by inhibitors of carnitine/organic cation transporter (OCTN2), such as carnitine analogues and cationic compounds. In RT-PCR analysis, OCTN2 expression was detected. These results demonstrated that the high-affinity carnitine transporter OCTN2, which is localized at the basolateral membrane of epididymal epithelial cells, mediates carnitine supply into those cells from the systemic circulation as the first step of permeation from blood to spermatozoa.Reproduction (

Hypoxia-induced apoptosis and mechanism of epididymal dysfunction in rats with left-side varicocele

“…Epididymal carnitine and sialic acid are important indicators of epididymal microenvironment and function. Carnitine plays an important role in sperm count, maturation and motility in the epididymis (Ng et al ., ; Kobayashi et al ., ). Besides, carnitine could be used to evaluate the infertile male as its value positively correlated with the number of spermatozoa, the percentage of motile spermatozoa and the percentage of normal forms (Matalliotakis et al ., ).…”

Xenobiotic transporter expression along the male genital tract

“…Additionally, transporters that contribute to the microenvironment of the MGT, such as those controlling pH or calcium concentrations, have also been studied [49–50]. OCTN2 has also been characterized for its ability to transport carnitine, an important nutrient for male fertility, in MGT tissues [51]. Several ABC transporters have also been implicated in cholesterol transport within the testis, spermatozoa, and epididymis [52–55].…”

Paradoxical increase of sperm motility and seminal carnitine associated with moderate leukocytospermia in infertile patients

“…Pena et al (43) have already published similar results for another epididymal marker, neutral alpha-glucosidase. The epididymal epithelium uptakes circulating carnitine in blood via an androgen-dependent mechanism involving OCTN2, an Na þ -dependent specific receptor located in the basal pole of epithelial cells (44). Carnitine uptake increases in proportion to the flow rate of viable spermatozoa through the epididymis (45,46).…”