Potassium exchange between cerebrospinal fluid, plasma, and brain.

CSERR, HELEN. Potassium exchange between cerabrospinal @id, plasma, and brain. Am. J. Physiol. 2og(6): I2Ig--I226* 1965*Potassium exchange between cerebrospinal fluid (CSF), plasma, and brain was investigated in anesthetized dogs and rats using the technique of ventriculocisternal perfusion. Transport via bulk secretion and absorption of CSF accounts for only 20% of total potassium exchange, unidirectional ionic fluxes across the ependyma for 80 TO. This large transependymal exchange is primarily between CSF and brain intracellular potassium pools, since two-thirds of the K42 outflux can be recovered from brain tissue. Conversely, much of transependyma1 influx comes from brain, as demonstrated by the low specific activity of influx relative to that of plasma following intravenous injection of K 42. Potassium outflux is almost: proportional to CSF [Kf] in the range O-IO mEq/liter but is independent of plasma [K’J. Perfusion with IO-~ M ouabain reduces transependymal K42 outflux to 25% of control; the residual outflux may be accounted for by passive processes. Results are discussed in terms of I) regulation of CSF potassium concentration and 2) the relationship between CSF and brain extracellular fluid.