P-glycoprotein expression in human major and minor salivary glands

Sodium pump and carbonic anhydrase activity have been described in the sali vary glands. However, it remains to be elucidated whether these energy sour ces are used for secretion, excretion or both. In addition, the differences in the function of excretion and the role of the excretory duct cells are currently unknown in salivary glands. Expression of P-glycoprotein (P-gp), which is an ATPase-binding efflux pump, was tested in normal major and mino r salivary glands from humans. P-gp was distributed on the basolateral memb rane of serous acinar cells in the major salivary glands and the minor sali vary glands. In particular, it was found to be present on the basolateral m embrane and cytoplasm of acinar demilunar cells in the anterior lingual gla nd. Intense expression was identified in the basolateral membrane of the st riated duct cells of the major salivary glands. P-gp was distinctly positiv e in the basolateral and/or luminal membranes of the initial part and in th e luminal membrane of the terminal part of the excretory duct cells of the major salivary glands, whereas it was positive in the luminal membranes of both the initial part and the terminal part of the excretory duct cells of the minor salivary glands. These disparate distributions between the major and the minor salivary glands suggest different physiological excretions in the striated duct. P-gp may be physiologically involved in an important pa rt of the transporter system, not only in the acinar serous cells and the s triated duct cells, but also in the excretory duct cells in the salivary gl ands. (C) 2001 Elsevier Science Ltd. All rights reserved.