Brain maturation and high-energy phosphate diffusivity: alteration in cytosolic microenvironment and effective viscosity.

Maturational changes in intracellular brain phosphocreatine (PCr) transport were investigated using 31P-nuclear magnetic resonance diffusion spectroscopy. The diffusivities of PCr showed significant maturational facilitation in rat brain in vivo. Physicochemical analysis of the cytosol microenvironment as a multicomponent solution, where one of the components is a dilute polymer, indicated that the observed developmental facilitation of PCr diffusivity is likely to be due to a decline in the concentration of the free amino acid taurine. Changes in the concentrations of biopolymers (i.e., proteins or lipids) have only little effect, if any, on PCr diffusivity. PCr diffusivity values of rat brain measured in vivo showed excellent quantitative agreement with the predicted values estimated using a model for multicomponent diffusion. The study confirmed that the taurine/N-acetylaspartate exchange observed during postnatal development of rat brain plays a major, it not unique, role in maturational facilitation of intracellular high-energy phosphate transport.