Acute barrier perturbation abolishes the ca(2+) and k(+) gradients in murine epidermis: Quantitative measurement using PIXE

Epidermal permeability barrier homeostasis requires the delivery of lipids and hydrolytic enzymes by lamellar body exocytosis from the uppermost granu lar cells, a process that is upregulated following barrier disruption. As l amellar body secretion is controlled by ionic concentrations, especially Ca 2+ and K+, we used a quantitative technique, microbeam proton-induced X-ray emission, to measure Ca2+, K+, Cl-, and P concentrations before and after acute barrier perturbation by acetone applications, We found a steep gradie nt of Ca2+ in normal tissue, peaking in the outer stratum granulosum, which disappeared after barrier disruption, and partially reformed as the barrie r recovered. A similar gradient, peaking somewhat lower in the epidermis (i .e., at the stratum granulosum-stratum corneum interface), was found for K. Epidermal concentrations of K+ also decreased after barrier abrogation, a lthough to a lesser extent than Ca2+. In contrast, P and Cl- demonstrated d istribution gradients at baseline, which remained unchanged after barrier d isruption. These studies quantitate the levels of Ca2+, K+, Cl-, and P with in specific epidermal cell layers at baseline, and in relation to changes i n permeability barrier integrity. Ca2+ and K+, but not Cl- or P, decrease a fter barrier disruption, consistent with these two ion's role in barrier re pair.