The purinoceptor agonist ATP has been shown to induce sweating in the isolated eccrine sweat gland (Sato et al. 1994), implicating the P2Y class of receptor in sweat secretion. All P2Y receptor subtypes couple to phospholipase C and hence cause the mobilisation of intracellular calcium (Ca(2+i)). We have recently reported that there is an altered distribution of the P2Y receptor subtypes in hyperhidrotic eccrine sweat glands (Lindsay et al. 2003), a condition characterised by the production of an inappropriately large volume of sweat. There are no functional data regarding purinoceptors in these abnormal glands. Here we have investigated the increases in [Ca²⁺]_i elicited by ATP and UTP, in both normal and hyperhidrotic sweat gland cells.

Skin biopsies were obtained with informed consent and local medical ethical committee approval from patients with no apparent skin disease and from those suffering from hyperhidrosis. Freshly isolated glands were obtained using the method of Lee et al. (1984) and were cultured and maintained using standard techniques. Primary culture cells grown on glass coverslips were loaded with the calcium-sensitive fluorescent dye, Fura-2 AM (3 µM) for 15 min at 37 °C. The dye was excited at 340 and 380 nm and the fluorescence ratio (340:380) detected at 512 nm. Cells were superfused with Hepes-buffered salt solution (mM): NaCl (130), KCl (5), MgCl₂ (1), CaCl₂ (1), Hepes (20), glucose (10), pH to 7.4 at 37 °C. Agonists were also diluted in the Hepes-buffered solution. Values are means ± S.E.M. Statistical analyses were carried out using Student’s unpaired t test, with P < 0.05 taken to be significant.

ATP produced a concentration-dependent increase in free cytosolic calcium with a pEC₅₀ of 5.32 ± 0.10 in normal cells (n = 5) and 5.53 ± 0.10 in hyperhidrotic cells (n = 4). In normal cells a maximal concentration of 100 µM ATP evoked an increase in [Ca²⁺]_i of 0.41 ± 0.05 ratio units (n = 8). Hyperhidrotic cells produced an increase of 0.78 ± 0.23 ratio units (n = 4) in response to 100 µM ATP, which was significantly greater than normal (P < 0.05). In contrast to ATP, UTP was significantly more potent in hyperhidrotic cells, pEC₅₀ of 5.78 ± 0.04 (n = 4), compared to normal cells, 4.89 ± 0.14 (n = 5, P < 0.001). In normal cells a maximal concentration of 100 µM UTP caused an increase in [Ca²⁺]_i of 0.30 ± 0.05 ratio units (n = 7), which was significantly less than that found in hyperhidrotic cells, 0.96 ± 0.34 ratio units (n = 4, P < 0.05).

These results show that in cultured human sweat gland cells there exist purinoceptors that respond to both ATP and UTP, suggesting the presence of at least the P2Y₂ receptor subtype. However in cultured hyperhidrotic cells there is a receptor population that is more sensitive to UTP than ATP. Since it is the P2Y₄ receptor subtype that is activated preferentially by UTP, it is possible that this receptor has involvement in the excessive sweat production associated with hyperhidrosis.