To understand the role of Na+/H+ exchanger 1 (NHE1) in intracellular pH (pH
(i)) regulation and neuronal function, we took advantage of natural knockou
t mice lacking NHE1, the most ubiquitously and densely expressed NHE isofor
m in the central nervous system (CNS). CA1 neurons from both wildtype (WT)
and NHE1 mutant mice were studied by continuous monitoring of pH(i), using
the fluorescent indicator carboxy-seminaphthorhodafluor-1 (SNARF-1) and con
focal microscopy. In the nominal absence of CO2/HCO3-, steady-state pH(i) w
as higher in WT neurons than in mutant neurons. Using the NH4Cl prepulse te
chnique, we also show that H+ flux in WT neurons was much greater than in m
utant neurons. The recovery from acid load was blocked in WT neurons, but n
ot in mutant neurons, by removal of Na+ from the extracellular solution or
by using 100 mu M 3-(methylsulfonyl-4-piperidinobenzoyl)-guanidine methanes
ulfonate (HOE 694) in HEPES buffer. Surprisingly, in the presence of CO2/HC
O3-, the difference in H+ flux between WT and mutant mice was even more exa
ggerated, with a difference of more than 250 mu M/s between them at pH 6.6.
H+ flux in CO2/HCO3- was responsive to diisothiocyanato-stilbene-2,2'-disu
lfonate (DIDS) in the WT but not in the mutant. We conclude that (a) the ab
sence of NHE1 in the mutant neurons tended to cause lower steady-state pH(i
) and, perhaps more importantly, markedly reduced the rate of recovery from
an acid load; and (b) this difference in the rate of recovery between muta
nt and WT neurons was surprisingly larger in the presence, rather than in t
he absence, of HCO3-, indicating that the presence of NHE1 is essential for
the regulation and/or functional expression of both HCO3--dependent and -i
ndependent transporters in neurons.