Exchange of calcium between blood, brain, and cerebrospinal fluid

Abstract

Ca exchange was measured in anesthetized cats during steady-state ventriculocisternal perfusions. When Ca⁴⁵ was added to the perfusate the efflux coefficient from CSF averaged 0.025 ml/min of CSF cleared of Ca⁴⁵. This coefficient was independent of CSF Ca concentration, indicating passive diffusion. About onethird of this isotope was recovered in brain tissue, two-thirds presumably diffused into blood. The brain radioactivity was localized to areas immediately adjacent to the CSF pathway. When the isotope was given systemically, the efflux coefficient into the ventricular system averaged 0.015 ml/min of serum effectively cleared of Ca⁴⁵. In these experiments the specific activity of the CSF approached that of the serum. At the same time the specific activity of the brain Ca was low. Hence, the chief source of the Ca entering CSF must be blood. The rate of movement of Ca⁴⁵ from blood to CSF was not altered when CSF formation was suppressed by adding acetazolamide or lowering the pH of the perfusate. This suggests that Ca transport is independent of the bulk fluid formation.