CL- HCO3- EXCHANGE FUNCTION DIFFERS IN ADULT AND FETAL-RAT HIPPOCAMPAL-NEURONS/

We studied Cl-/HCO3- exchange function in acutely dissociated single h ippocampal neurons from adult and fetal day 18 rat using a fluorescent intracellular pH (pH(i)) indicator dye. The presence of Cl-/HCO3- exc hange activity was assayed by observing the elevation in pH(i) upon ac ute reversal of the Cl- gradient. Resting intracellular pH in acutely dissociated neurons of both adult and fetal tissue was significantly h igher than that of cultured fetal hippocampal neurons (day 10-12 in cu lture). Acute removal of extracellular Cl- caused a rapid and reversib le increase in pH(i) by 0.25 pH units in adult neurons but had virtual ly no effect in similarly dissociated fetal neurons. Cl-/HCO3- exchang e activity was also undetectable in fetal cultured hippocampal neurons . The mRNA for the anion exchanger AE3 is expressed abundantly in adul t rodent neurons. AE3 is a potential candidate molecule for the observ ed Cl-/HCO3- exchange activity. In situ hybridization was used to moni tor expression of the AE3 gene in these two age groups. We found that both adult and fetal neurons express AE3 mRNA. These results indicate that AE3 may not function as a Cl-/HCO3- exchanger in fetal neurons, i n contrast to its possible role in the adult brain.