Effects of UTP on Na+, Cl− and K+ transport in primary cultures from human sweat gland coils

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Abstract
Extracellular ATP and UTP can increase membrane permeability in the sweat gland, but the intracellular signalling regulating the response to these agonists is poorly understood. Stimulation of Cl− transport by nucleotides has been suggested as a pharmacological therapy to improve Cl− secretion in patients with cystic fibrosis. In the present study, regulation of Na+, Cl− and K+ transport in primary cultures of cells from the secretory coil of human sweat glands was investigated by electron probe X-ray microanalysis. Stimulation with 200 μM UTP for 2 min at room temperature caused a significant increase in intracellular Na but did not affect Cl and K. After 5 min, the Na concentration was still increased, but now also a significant decrease in Cl and K was observed, indicating an increase in Cl− and K+ permeability. The effect of UTP on Cl− secretion was enhanced in Mg2+-deficient buffer, indicating that the response is elicited by the extracellular fully ionized form of UTP (UTP4+), but not by MgUTP2+. The effects of UTP were abolished in Ca2+-deficient buffer supplemented with EGTA. Alloxan, an adenylate cyclase inhibitor, did not inhibit the response to UTP. These results indicate that the membrane Cl− and K+ permeability elicited by UTP in primary coil cell cultures is Ca2+-dependent. The response to UTP did not attenuate at 8 ∘C, suggesting that it could be activated, in part, via ligand-gated ion channels. The effect of UTP was not decreased in the presence of ouabain. Pre-treatment of the cells with pertussis toxin (24 h) had minor effects on Cl− secretion activated by UTP, indicating a role for G proteins in the UTP activation of Cl− secretion.