N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W7) stimulation of K+ transport in a human salivary epithelial cell line.
Treatment of a human salivary epithelial cell line, HSG-PA, with the calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W7; 20-70 microM) increased 86Rb (K+) influx and efflux in a manner similar to that resulting from muscarinic (carbachol; Cch) or calcium ionophore (A23187) stimulation. Unlike the Cch or A23187 responses, the W7 responses were not blocked by 0.1 mM atropine (muscarinic antagonist) or phorbol-12-myristate-13-acetate (0.1 microM). Like Cch- or A23187-stimulated 86Rb fluxes, W7-stimulated 86Rb fluxes were substantially blocked by the K+ channel inhibitors quinine (0.25 mM) and scorpion venom-containing charybdotoxin (33 micrograms/mL), while 5 mM tetraethylammonium chloride (K+ channel blocker), furosemide (0.1 mM; Na+,K+,2Cl- co-transport inhibitor) and ouabain (10 microM; Na+,K(+)-ATPase inhibitor) were ineffective. Purified charybdotoxin (10 nM) also blocked W7-stimulated 86Rb influx, as well as 86Rb influx stimulated by Cch or A23187. Although Quin 2 fluorescence measurements indicated that W7 increased free intracellular Ca2+ concentration ([Ca2+]i), the magnitude of the increase appeared to be insufficient to solely account for the W7-stimulated increases in 86Rb fluxes (i.e. K+ channel activity). Ca2+ was involved in the W7 response, however, as lack of Ca2+ in the incubation medium reduced the W7-stimulated increases in 86Rb influx and efflux. Taken together, our results suggest that W7 increased K+ fluxes in HSG-PA cells by interacting, directly or indirectly, with the K+ transport machinery (K+ channels) in a manner different from that observed during muscarinic stimulation, and also in a manner not accounted for solely by the formation of a typical muscarinic- or calcium ionophore-generated calcium signal.