Na+-H+ exchangers mediate the uptake of sodium in exchange for an intracellular proton and are thought to be involved in cell volume regulation, fluid secretion and absorption, and pH homeostasis. Our laboratory has previously cloned nine nematode Na+-H+ isoforms
nhx-1 through
nhx-9 and determined expression patterns for each isoform using promoter::GFP transgene reporter constructs. Nhx-2 is a Na+-H+ exchanger expressed exclusively at the apical membrane of intestinal cells. We report here functional coupling of
nhx-2 activity with nutrient uptake in the intestine. The effect of
nhx-2 RNAi was a dramatic delay in development, while the adult worms were incapable of producing viable offspring, resulting in a maternal lethal phenotype. In addition,
nhx-2 worms lived approximately 50% longer that wild-type. These deficits were reminiscent of the effects of starvation, an observation buoyed by the results of Nile Red staining, which suggested that
nhx-2 may be functionally coupled to fat uptake or metabolism. Opt-2 is a proton-coupled oligopeptide transporter known to be involved in fat accumulation in the intestine, and the activity of
opt-2 is driven by a transepithelial proton gradient. Nhx-2 and
opt-2 proteins were coincidentally expressed, and RNAi of
opt-2 led to a maturation phenotype resembling
nhx-2 alone, though not as severe. In order to explore this potential functional interaction, we developed a system to assess pH in a living organism under physiological conditions. pHlourin, a pH-sensitive form of GFP used for ratiometric imaging, was expressed in the intestine, and real-time fluorescent imaging was used to track pH changes upon exposure to Gly-Sar, a model substrate for oligopeptide transporters. Gly-Sar in the absence of sodium caused an intestinal acidification of approximately 0.3 pH units that was reversible upon sodium readdition. In contrast, in the
nhx-2 RNAi treated nematodes, Gly-Sar addition did not result in acidification, but the resting pH of the intestine was found to be 0.3 pH units lower than in wild-type nematodes. RNAi of
opt-2 also abolished Gly-Sar induced acidification, but the resting pH was near normal. These results demonstrate directly that knockdown of
nhx-2 results in a pH change in the intestine that negates the ability of
opt-2 to take up oligopeptides. The increased severity of the
nhx-2 phenotype may be the result of perturbing additional pH-coupled nutrient uptake processes. Our data is the first to demonstrate that a Na+-H+ exchanger is required for effective nutrient absorption in an intact, living organism, and can influence aging, as well. This work lays a foundation for examining acid-base physiology from the cellular to the systems level.