Jh. Pizzonia et al., CHARACTERIZATION OF NA+ H+ EXCHANGE ACTIVITY IN CULTURED RAT HIPPOCAMPAL ASTROCYTES/, Journal of neuroscience research, 44(2), 1996, pp. 191-198
Astrocytes actively maintain their intracellular pH (pH(i)) more alkal
ine than expected by passive distribution of H+, Acid extruding transp
orters such as the amiloride-sensitive Na+/H+ exchanger (NHE) are nece
ssary for pH regulation, Currently, four mammalian NHEs (NHE1-NHE4) ha
ve been cloned, with a fifth (NHE5) partially cloned, We attempted to
determine which isoform(s) of NHE was present in cultured hippocampal
astrocytes using amiloride sensitivity and immunospecificity as criter
ia, In the absence of HCO3-, amiloride blocked pH(i) recovery after an
acid load with an IC50 of similar to 3.18 mu M, similar to values rep
orted for the amiloride-sensitive isoforms NHE1 and NHE2, Immunoblotti
ng with a highly specific antibody for NHE1 identified a 100 kDa prote
in, indicating the presence of NHE1 in whole brain, hippocampus, and c
ultured hippocampal astrocytes, Further probing for an additional amil
oride-sensitive NHE failed to detect evidence of the presence of NHE4.
Surprisingly, application of the potent analog of amiloride, ethyliso
propylamiloride (EIPA), caused a reversible alkalinization of pH(i), s
uggesting the presence of an additional acid/base transport mechanism
that is EIPA-sensitive. (C) 1996 Wiley-Liss, Inc.