ELECTRICAL POTENTIAL OF CEREBROSPINAL FLUID

Abstract

Cerebrospinal fluid is normally about 5 mV positive to blood in unanesthetized goats and in anesthetized dogs. Normal csf [cerebrospinal fluid]: plasma concen. tration ratios of Na+ and Mg++ are greater than predicted for passive equilibrium in this electric field; the ratios for HCO3- and K+ are less than predicted. The csf potential varies linearly with arterial pH, changing from about + 15 mv at ph 7.1 to -3 mV at pH 7.6. The P.D. varies inversely with [K4] in fluid perfusing the ventriculocisternal system but is independent of plasma [K+]; it is unaffected by changes in [HCO3-], [H+], [Na+] or [Cl~] in csf. Rate of secretion of csf remains almost unaltered during large changes of P.D. produced by acidosis. Rates of penetration of K42, Na24 and Cl36 from blood to brain tissue are not significantly altered by acidosis or alkalosis, thus suggesting that changes in csf potential do not affect transport of these ions between blood and brain. The origin of the P.D. remains unknown, but it must affect to some degree the steady-state concentration ratios of all ions distributed between csf and plasma.