Cellular expression of a monocarboxylate transporter (MCT1) in the mammary gland and sebaceous gland of mice.

Proton-coupled monocarboxylate transporters (MCTs) are essential for the transport of lactate, ketone bodies, and other monocarboxylates through the plasma membrane, but the direction and substrates of transporting in loco remain unclear. The present study examined the expression and subcellular localization of MCTs in lipogenic organs. An in situ hybridization survey of major MCT subtypes detected an intense expression of MCT1 mRNA in the mammary gland, Harderian gland, and sebaceous gland. The MCT1 immunoreactivity was found baso-laterally in acinar cells of the mammary and Harderian glands. Alveolar cells of sebaceous glands in the skin, eyelids, and penis contained the membrane-associated MCT1 immunoreactivity along the entire length of the cell surface at the margin of alveoli. These MCT1-expressing exocrine glands possessed more abundant transcripts of acetyl-CoA carboxylase-1, a key enzyme for lipogenesis, than did representative lipogenetic organs such as the liver. Since the secretions from these glands contain fat as a major product, the cellular localization of MCT1 suggests the involvement of the transporter in the uptake of lactate, acetate, and other monocarboxylates for production of medium- and long-chain fatty acids.