Buffer capacity of rat cortical tissue as well as of cultured neurons and astrocytes

Abstract

The primary objective of this work was to assess the intrinsic nonbicarbonate buffer capacity (β i) of cultured neurons and astrocytes an d to compare the β i values obtained to those of neocortical tissue. A second objective was to determine the pH dependence of β i. Titration of homogenates of whole-brain cortical tissue and cultured neurons with NaOH and HC1 gave β i values of 25–30 mmol·1 −1·pH −1. The buffer capacity was essentially constant in the pH range of 6–7. Astrocytes showed a higher buffer capacity and a clear relationship between β i and pH. However, βini decreased when pH reduced from 7 to 6. The β i values derived from microspectrofluorometric studies on neurons and astrocytes were suprisingly variable, ranging from 10 to 50 mmol·1 −1·pH −1. The ammonia “step method” suggested that β i increased dramatically when pH was lowered from 7 to 6 but the propionic “step method” failed to reveal such a pH dependence. Some techniques obviously give erroneous values for β i, presumably because changes in buffer base concentration (due to transmembrane fluxes of H +, HCO − 3, NH 4 + or anions of weak acids) violate the principles upon which the calculations are based. From the results obtained by direct titration and with the propionate technique, we tentatively conclude that β i in neurons and astrocytes are ≈20 and 30 mmol·1 −1·pH −1, We further suggest that the term “intrinsic buffer capacity”, as commonly used, isredefined.