Thermoregulatory sweating in humans is known to be primarily a function of human eccrine sweat glands within the skin. The purinoceptor agonist ATP has been shown to induce sweating (Sato et al. 1991) and increase intracellular calcium in both freshly dissociated cells (Clunes et al. 1999) and primary culture cells from human glands (Bovell et al. 2000). These effects have been ascribed to the presence of purinoceptors of the P2Y class. There are five subtypes of the P2Y family (Burnstock, 1997); however, to our knowledge the subtype (s) present in human sweat glands has never been investigated. Therefore, immunohistochemistry was employed to investigate the presence and localisation of the P2Y₁, P2Y₂ and P2Y₄ receptor subtypes in normal eccrine sweat glands.

Axillary skin biopsies were obtained, with informed consent and local medical ethical committee approval, from both male and female patients with no apparent skin disease. Samples were fixed and processed using standard techniques. Immunohistochemical staining was performed using rabbit antibodies raised against P2Y₁, P2Y₂ and P2Y₄ (Alomone Labs, Israel) employing the avidin-biotin complex (ABC) procedure (Vector Labs, UK). Sections were counterstained with haematoxylin, dehydrated, cleared, mounted and viewed using light microscopy.

In all samples analysed, P2Y₁, P2Y₂ and P2Y₄-like immunoreactivity elicited the same pattern of apical membrane staining in the reabsorptive duct of the eccrine gland (n = 5). Citrate buffer antigen retrieval in addition revealed nuclear staining of both layers of ductal cells with P2Y₂ antibody (n = 6), which was not found with P2Y₁ and P2Y₄. The secretory coil was shown to contain highly specific staining of the outer layer of myoepithelial cells with both P2Y₂ and P2Y₁ (n = 11 and n = 6, respectively), whereas P2Y₄ staining was localised to a single cell type resembling that of the clear cells of the secretory coil (n = 5). Pre-absorption of antibodies with the appropriate control peptide abolished all staining.

Regulation of sweat secretion has always been attributed to the appropriate receptor occupancy on the basolateral membrane; however, the presence of apical purinoceptors in the eccrine sweat gland is suggestive of apical regulation of sweat secretion and absorption, as has been shown to be important in colonic epithelia (Cliff & Frizzell, 1990). These results imply that apical purinoceptors in the duct may play a role in the control of sweat reabsorption. The clear cells of the secretory coil are thought to be predominantly involved in sweat secretion and the localisation of the P2Y₄ subtype in these cells would suggest that this receptor is implicated in sweat secretion. The myoepithelial cells are not regarded as being involved in either secretion or reabsorption of sweat but are instead thought to provide support for the secretory coil during secretion. The presence of purinoceptors suggests that the support these cells provide may also be activated by purinergic agonists.

S.L.L. is supported by a Glasgow Caledonian University research studentship.

All procedures accord with current local guidelines.