Effects of UTP on Na+, Cl- and K+ transport in primary cultures from humansweat gland coils

Extracellular ATP and UTP can increase membrane permeability in the sweat g land, but the intracellular signalling regulating the response to these ago nists is poorly understood. Stimulation of Cl- transport by nucleotides has been suggested as a pharmacological therapy to improve Cl- secretion in pa tients with cystic fibrosis. In the present study, regulation of Na+, Cl- a nd K+ transport in primary cultures of cells from the secretory coil of hum an sweat glands was investigated by election probe X-ray microanalysis. Sti mulation with 200 mu M UTP for 2 min at room temperature caused a significa nt increase in intracellular Na but did not affect CI and K. After 5 min, t he Na concentration was still increased, but now also a significant decreas e in CI and K was observed. indicating an increase in Cl- and K+ permeabili ty. The effect of UTP on Cl- secretion was enhanced in Mg2+-deficient buffe r, indicating that the response is elicited by the extracellular fully ioni zed form of UTP (UTP4+), but not by MgUTP2+. The effects of UTP were abolis hed in Ca2+-deficient buffer supplemented with EGTA. Alloxan, an adenylate cyclase inhibitor, did not inhibit the response to UTP. These results indic ate that the membrane Cl- and K+ permeability elicited by UTP in primary co il cell cultures is Ca2+-dependent. The response to UTP did not attenuate a t 8 degrees C, suggesting that it could be activated, in pari, via ligand-g ated ion channels. The effect of UTP was not decreased in the presence of o uabain. Pre-treatment of the cells with pertussis toxin (24 h) had minor ef fects on Cl- secretion activated by UTP, indicating a role for G proteins i n the UTP activation of Cl- secretion.