Abstract
Skin is the largest organ of the body and acts as the first line of defense against the outside environment. The skin surface area of a male adult of 70 kg is approximately 1.80 m2. Skin is comprised of three distinct layers: the epidermis, the dermis and the subcutaneous fat. The epidermis is a multi-stratified epithelium, the apical part of which is the stratum corneum. The stratum corneum consists of several layers of corneocytes that form the primary barrier to body water loss. Nevertheless a total of about 350 ml/24h of water is lost through skin surface by perspiratio insensibilis (unnoticed perspiration), not including secretion from sweat glands (Nislon 1977). Keratinocytes are the major cell type of viable layers of the epidermis and synthesize keratin which plays a major role in epidermis function. Keratin is characterized by its insolubility, its high sulfur content (cystein and cystin residues) and its conspicuous affinity for water. When corneocyte keratin is deprived of its water the tissue becomes brittle and breaks easily (Blank et al. 1953). The epidermis water content drops sharply beneath the stratum corneum. Although it is established that the stratum corneum is the primary barrier to transepidermal water transport in the epidermis (Scheuplein et al., 1976), little is known on fluid transport within viable layers in the epidermis. The presence of aquaporin-3 (AQP3) was reported in rat skin (Frigeri et al. 1995). The purpose of this work was to investigate the presence of aquaporins in human skin and to study their role in water movements in the epidermis.