Taurine levels and localisation in the stratified squamous epithelia

The content and distribution of the amino acid taurine in squamous epithelia were studied using high-performance liquid chromatography and immunohistochemical methods. Quantitative analysis demonstrated that taurine was highly concentrated in the epidermis (5.49 mumol/g fresh tissue in the hairless skin of the hind footpad of the rat), although the values in the isolated stratum corneum were extremely low (< 0.073 mumol/g in the horny layer of the same skin area). No other analysed amino acid (such as glutamate, glutamine, glycine or alanine) showed this specific pattern of distribution. The immunohistochemical study revealed that in the dog and rat epidermis, taurine was present in the keratinocytes of the granular and upper spinous layers. The basal layer, lower spinous layer and stratum corneum were immunonegative. A similar immunostaining pattern was found in the epithelia of the different organs studied: the mouth, tongue and oesophagus of the dog and rat, the rat forestomach and the rat corneal epithelium. Other cell types, such as sebaceous and muscle cells, were immunolabelled. The existence of a circulating pool of taurine in the epidermis (via taurine release from keratinocytes before they reach the horny layer and its uptake by nearby cells) and its possible roles in these cells are discussed.