Transfer of Potassium Between Blood, Cerebrospinal Fluid and Brain Tissue

¹ From the Radioisotope and Research Laboratories, Veterans Administration Hospital and Department of Biochemistry, Vanderbilt University, Nashville, Tennessee

Anesthetized dogs were injected with radioactive potassium. After intravenous injection the appearance of the ions in cerebrospinal fluid was a summation of two exponentials with the maximum at about 30 minutes. The ratio of radioactivities of brain tissue to cerebrospinal fluid was stabilized at 120 minutes, whereas the ratio of cerebrospinal fluid to plasma reached this state after 30 minutes. After intracisternal injection the disappearance of K⁴² from cerebrospinal fluid was described by two exponentials. The activity in the plasma reached a maximum at 10–15 minutes and thereafter paralleled the disappearance curve from cerebrospinal fluid. Brain tissues did not reach equilibrium. These data have been compared with those obtained using radioactive sodium and bromide and discussed in relation to cerebrospinal fluid formation.