Two consequences of cerebral ischemia are cell acidification and cytotoxic edema. To test the possibility that Na+/H+ exchange mediates acid-induced edema, we measured cytoplasmic pH (pHi) and cell volume changes in C6 glioma cells that were artificially acid-loaded using weak electrolytes. pHi was monitored fluorimetrically with 2',7'-bis-(2-carboxyethyl)-5,6-carboxyfluorescein. Upon acidification with sodium propionate, pHi dropped to 6.74 +/- 0.05 (n = 25), and then recovered to levels near the physiological value of 7.23 +/- 0.02 (n = 13). Cell volume, measured by electronic sizing, increased concomitantly by approximately 50% in sodium propionate solution. Both pHi recovery and cell swelling were Na+-dependent, amiloride-sensitive, and inhibited at pHo less than 6.0. These results demonstrate that in vitro: (1) intracellular acidification can lead to cell swelling, and (2) pHi recovery and the concomitant cell swelling are likely mediated by Na+/H+ exchange. These mechanisms may be related to postischemic cytotoxic glial edema.