Slowly Changing Bioelectric Potentials Associated With the Blood-Brain Barrier

Abstract

A slowly changing bioelectric potential difference (P.D.) is measured in rats, rabbits, cats and dogs between various regions of the central nervous system (CNS) and the blood within the jugular vein. It is shown that the CNS-blood P.D. is very sensitive to alterations in alveolar CO₂ tension, but this relationship is dependent upon the H⁺ concentration rather than CO₂ per se. Whereas increasing intravenous H⁺ concentration increases CNS positivity, topical application of acid solutions directly to the cerebral cortex decreases CNS positivity. The same relationship is found for intravenous and topical K⁺. Anoxia and circulatory failure produce CNS negative deflections, often exceeding 15 mv, which do not return to zero for over 24 hours after death. Simultaneous measurements of arterial blood pH, cerebral cortex pH and CNS-blood P.D. reveal the following relationship among these variables: ΔP.D. = κ Δ log₁₀ [H⁺]_a/[H⁺]_i where [H⁺]_a is the H⁺ concentration of the arterial blood and [H⁺]_i is the H⁺ concentration of the CNS interstitial fluid. For the CNS-blood P.D. between cerebral cortex and jugular blood of rabbits and rats, κ is found to be 29 ± 5. These results are interpreted as indicating a source of emf across the pan-vascular blood-brain barrier which resembles a membrane diffusion potential. The blood-brain barrier is postulated to be more permeable to H⁺ and K⁺ than to anions and other cations.