Hydrogen ion buffering during complete brain ischemia.

As a first step to quantify [H+] changes in brain during ischemia we used H+-selective microelectrodes and enzyme fluorometric techniques to describe the relationship between interstitial [H+] ([H+]o) and peak tissue lactate after cardiac arrest. We found a step function relationship between [H+]o and tissue lactate rather than the linear titration expected in a homogeneous protein solution. Within a blood glucose range from 3-7 mM, brain lactate rose from 8-13 mmol/kg along with a rise in [H+]o of 99 +/- 6 nM(0.44 +/- 0.02 pH). At higher blood glucose levels (17-80 mM), brain lactate accumulated to levels of 16-31 mmol/kg; concurrently [H+]o rose by 608 +/- 16 nM (1.07 +/- 0.02 pH). The unchanging level of [H+]o between 8-13 and 16-31 mmol/kg lactate implies that [H+]o is at a steady-state, but not equilibrium with respect to [H+] in other brain compartments. We propose that ion-transport characteristics of astroglia account for the observed relationship of [H+]o to tissue lactate during complete ischemia and suggest that brain infarction develops after plasma membranes in brain cells can no longer transport ions to regulate [H+].