Resistance of astrocyte electrical membrane properties to acidosis changes in the presence of lactate.

The membrane potential and input resistance of mouse astrocytes in primary cultures were measured with two-channel microelectrodes. It was found that 30 mM sodium lactate (no pHo change) caused a hyperpolarization of 5 mV. A stepwise reduction in pH via HCl addition had no effect at pHo 6.5, at pHo 5.5 there was a 5 mV depolarization and at pHo 4.5 the membrane depolarized by 28 mV and the input resistance increased by 4.9-times. After 20 min this change was still reversible. If the pHo was lowered by the addition of lactic acid, a pHo of 4.5 (30 mM lactic acid) caused a 45 mV depolarization and a 4.3-times increase in input resistance. Exposure to these conditions caused irreversible effects. The exposure time for a 50% recovery of the membrane potential was 15 min. The results show that external acidification (for a period of 20 min) is only irreversible if lactate is present, probably due to excessive H+ shifts into the cells via the H+-lactate carrier. The results are of significance to explain glial damage during incomplete ischemia.