ABSTRACT
Calcium is the most abundant metal among the elements and the fifth most abundant element in the body. It holds a special place in animal physiology and cell biology. Together with phosphate, Ca is the major constituent of the endoskeleton; about 99% of body Ca2 resides in bones and teeth. The balance, as mobile Ca2, is found throughout the body fluids, and is the most important mineral for general cellular function and for the regulation of a wide variety of biological activities. Calcium is an intracellular messenger in signal transduction, e.g., in the regulation of muscle contraction, insulin secretion, and cell growth and differentiation; all cells feature specific Ca2 transport systems. Many of these activities involve interactions with proteins to which calcium binds tightly and exerts a stabilizing, activating or modulating effect. These strong associations can lead to crosslinking and conformational changes (1). A versatile Ca-regulating protein present in every eukaryotic cell is calmodulin, a multipurpose intracellular Ca2 receptor possessing four calcium binding sites. Calmodulin mediates most Ca2-dependent processes in the skin including enzyme regulation, histamine release, T-lymphocyte activation, and platelet aggregation, critical factors in the process of wound healing of the skin (2). A specific Ca-binding protein has been identified in the human epidermis (3). A large Ca2 concentration gradient exists across the cell membrane, serum calcium being approximately 1 mM, while free Ca2 in keratinocytes is approximately 100 nM (4).
