The CSF/Blood Potential in Sustained Acid‐Base Changes in the Rat. With Calculations of Electrochemical Potential Differences for H+and HCO‐3

Abstract The electrical D.C. potential difference between cisternal cerebrospinal fluid and external jugular blood was measured in rats during sustained acid‐base changes. One group, serving as a control series, was given an artificial extracellular fluid i.p., while two other groups were made acidotic or alkalotic by means of i.p. injections of NH4Cl or NaHCO3 solutions. In the last two groups NH4Cl or NaHCO3 was given, but Con was simultaneously administered so as to keep either the plasma bicarbonate or the plasma pH constant. In all groups the CSF/ plasma potential was permanently changed in relation to the arterial plasma pH, but there was a larger potential change in alkalosis (about 50 mV/pH unit) than in acidosis (about 30 mV/pH unit). Calculations of electrochemical potential differences for H+and HCO3‐between CSF and plasma showed no significant differences in nonrespiratory acidosis and alkalosis but significant increases in hypercapnia. The results do not support the theory that an active H+transport regulates the CSF pH to constancy.