OCTN2-mediated transport of carnitine in isolated Sertoli cells

Abstract

Carnitine is extensively accumulated in epididymis. Carnitine is also accumulated in testis at higher concentration than in the plasma and is used in spite of the presence of the blood–testis barrier. In this study, we examined the characteristics of carnitine transport in primary-cultured rat Sertoli cells, which constitute a part of the blood–testis barrier. Uptake of [3H]carnitine (11.4 nM) from the basal side of Sertoli cells was Na+-dependent and was significantly decreased in the presence of 10 μM (48.0 ± 7.4% of control) or 100 μM unlabeled carnitine (14.6 ± 5.7% of control). Furthermore, the uptake was significantly inhibited in the presence of 100 μM acetyl-L-carnitine, 100 μM gamma-butyrobetaine or 500 μM quinidine. In RT-PCR analysis, the high-affinity carnitine transporter OCTN2 was detected in rat whole testis tissue and primary-cultured Sertoli cells. In contrast, the low-affinity carnitine transporter ATB0,+was detected in rat whole testis tissue, but not in primary cultured Sertoli cells. These results demonstrate that OCTN2 mediates carnitine supply to Sertoli cells from the circulation.