Intracellular Ca⁺⁺/Mg⁺⁺ Homeostasis during postnatal growth of experimental rats. Multiple time-point study

In most tissues, various cell membrane ion transporting systems are not fully developed and/or maximally active at the prenatal and early postnatal stage. Their progressive development and expression are a function of growth and maturity. We performed a multiple time-point study, in order to investigate the ability of a variety of tissues to maintain appropriate Ca⁺⁺ and Mg⁺⁺ homeostasis at different stages of postnatal development. Total intracellular Ca⁺⁺ in one-week-old rat liver, brain and spinal cord tissues was significantly elevated, compared to mature animals. It increased further through the first three weeks of gestation. Intracellular Ca⁺⁺ gradually and significantly declined in adult and mature animal groups. Alterations in total intracellular Mg⁺⁺ of the same tissue samples, although not so profound, paralleled changes in total intracellular Ca⁺⁺. We conclude that a developmental switch in intracellular Ca⁺⁺ and Mg⁺⁺ homeostasis occurs one to three weeks following birth. It might be related to the incomplete development of Ca⁺⁺ and Mg⁺⁺ transmembrane transporting systems, previously reported as being only partially expressed at the early postnatal stage. These developmental alterations in total intracellular Ca⁺⁺ and Mg⁺⁺ content might serve as a regulatory mechanism, adjusting cell activities to the physiological requirements of the growing and maturing animal.