A review of electron probe X-ray microanalysis studies of salivary gland cells.

Electron probe X-ray microanalysis (EPXMA) has now been successfully applied to several salivary gland preparations. This paper briefly reviews the principles underlying this technique and the specific sample preparation procedures which permit accurate measurement of elemental concentrations in the various intracellular spaces. Findings from salivary gland studies indicate that cytoplasmic and nuclear spaces of nonstimulated acinar cells have high concentrations of K and P, and low concentrations of Mg, Ca, and S; and that mature secretory granules have high concentrations of Ca and S, and relatively low concentrations of K and P. No consistent differences have been found between the elemental concentrations of mucous and serous secretory granules. In vivo and in vitro EPXMA studies of the elemental changes associated with secretory granule maturation indicate there are at least two stages in this process: an early stage during which granule S concentration increases in parallel with mass density as condensing vacuoles mature into secretory granules, and a late stage during which granule mass density and protein content increase with no further elemental concentration changes. Findings from other in vivo and in vitro studies indicate that secretory granule membranes are permeable to Na, K, and Cl ions because the granular concentrations of these elements are altered by electrochemical gradients. Recent EPXMA results indicate that cells stimulated with parasympathomimetic agonists have decreased K and Cl concentrations, and increased Na concentrations. Furthermore, the magnitude of these changes are quantitatively consistent with changes measured using radio-isotope equilibration and other techniques. In contrast, cells stimulated with the β-adrenergic agonist, isoproterenol, have increased concentrations of Na and Cl, but unchanged K concentrations. In terms of pathology, Na concentration is found to be elevated in secretory granules from labial salivary glands of patients with cystic fibrosis, but the pathophysiological consequences of this change are not known. Thus, studies utilizing EPXMA have obtained detailed and unique information about physiological and pathophysiological changes in elemental concentrations of intracellular organelles in salivary gland cells. © 1994 Wiley-Liss. Inc.