Electron probe X-ray microanalysis of cellular ions in the eccrine secretory coil cells during methacholine stimulation

Summary Intracellular concentrations of Na, K, Cl (Na], K] and Cl], respectively) and other elements were determined in isolated monkey eccrine sweat secretory coil cells using quantitative electron probe X-ray microanalysis of freeze dried cryosections. The validity of the methodology was partially supported by qualitative agreement of the X-ray microanalysis data with those obtained by micro-titration with a helium glow spectrophotometer. Na], K] and Cl] of the cytoplasm were the same as those in the nucleus in both clear and dark cells. Na], K], and Cl] of the clear cells were also the same as those of the dark cells at rest and after stimulation with methacholine (MCh), suggesting that these two cell types behave like a functional syncytium. MCh stimulation induced a pharmacologically specific, dose-dependent decrease in K] and Cl] (as much as 65%), and a 3.7-fold increase in Na]. In myoepithelial cells, a similar change in Na] and K] was noted after MCh stimulation although the decrease in Cl] was only 20%. The MCh-induced change in Na], K] and Cl] was almost completely inhibited by removal of Ca²⁺ from the medium. 10^–4 m bumetanide inhibited the MCh-induced increase in Na], reduced the decrease in K] by about 50%, but slightly augmented the MCh-induced decrease in Cl]. 10^–4 m ouabain increased Na] and decreased K] as did MCh; however, unlike MCh, ouabain increased Cl] by 56% after 30 min of incubation. Thus the data may be best interpreted to indicate that Ca-dependent K efflux and (perhaps also Ca-dependent) Cl efflux are the predominat initial ionic movement in muscarinic cholinergic stimulation of the eccrine sweat secretory coils and that the ouabain-sensitive Na pump plays an important role in maintenance of intracellular ions and sweat secretion.