THE REGULATION OF MEMBRANE I-125(-) AND RB-86(+) PERMEABILITY IN A VIRALLY TRANSFORMED-CELL LINE (NCL-SG3) DERIVED FROM THE HUMAN SWEAT GLAND EPITHELIUM

We have explored the factors that may regulate membrane permeability in a cell line (NCL-SG3) derived from the human sweat gland epithelium. Ionomycin increased the rate of I-125(-) efflux from preloaded cells and this action appeared to be due to an increase in intracellular free calcium ([Ca2+](i)). The ionomycin-evoked increase in I-125(-) efflux was reduced in cells that were exposed either to barium or to valinomycin in the presence of a high concentration of external potassium. It thus appears that a fraction of the ionomycin-evoked increase in I-125(-) efflux is due to the activation of potassium channels and experiments using Rb-86(+) also suggested that ionomycin increased the rate of potassium efflux, an effect which was totally abolished by barium. Blockade of Na+-K+-2Cl(-) cotransport and of Cl--HCO3- exchange reduced the basal rate of I-125(-) efflux and the ionomycin-evoked increase in I-125(-) efflux from control cells and from cells depolarized by valinomycin. These transport systems thus contribute to anion efflux, although [Ca2+](i)-dependent chloride channels also appear to be present. Acetylcholine increases [Ca2+](i) in the secretory cells of human sweat glands, but this neurotransmitter did not increase [Ca2+](i) in NCL-SG3 cells and so membrane permeability was not under cholinergic control. Adrenaline did not increase [Ca2+](i), but this hormone did evoke cyclic-3',5'-adenosine monophosphate (cyclic AMP) production. However, membrane permeability was not under adrenergic control, as the cells did not appear to express functional, cyclic AMP-dependent anion channels. This may be because they were not fully differentiated under the culture conditions. ATP consistently evoked a dose-dependent increase in anion efflux that appeared to be mediated by [Ca2+](i). The increase in [Ca2+](i) was initiated by the release of calcium from a limited internal store and was subsequently sustained by calcium influx. UTP and ADP also increased [Ca2+](i), whereas adenosine, AMP and alpha,beta-methylene ATP were without effect. These data thus suggest that a subclass of type 2 purine receptor, which is functionally coupled to phosphoinositidase C, is present in these cells.