Corneocytes undergo systematic changes in element concentrations across the human inner stratum corneum.

Using analytical electron microscopy of freeze-dried cryosections, physiologic elements were visualized within individual cells across the human inner stratum corneum. Human corneocytes undergo systematic changes in element composition as they advance through this region. Phosphorus is largely excluded from the stratum corneum, undergoing a precipitous drop in concentration at the granular/stratum corneum interface. The cellular potassium concentration has a profile similar to that of phosphorus but with a slower decline, thus migrating further into the stratum corneum. In contrast, the cellular chloride concentration increases in the innermost corneocyte layer, increases further in the subsequent layer or two (as potassium declines), and then decreases to values comparable to those in the innermost corneocyte. The cellular sodium concentration (per unit volume of tissue) is relatively unaltered in transit across the inner stratum corneum. The initial potassium and chloride movements are oppositely directed and have the appearance of creating an electrical charge imbalance. The position-dependent alterations in corneocyte elemental composition may reflect sequential stages of chemical maturation occurring intracellularly during stratum corneum transit, an example of which is the breakdown of filaggrin that occurs over this same region of the inner stratum corneum.