Sodium–hydrogen exchangers in the nematode Caenorhabditis elegans: investigations towards their potential role in hypodermal H+ excretion, Na+ uptake, and ammonia excretion, as well as acid–base balance

Abstract

Cation/proton exchangers of the cation proton antiporter 1 (CPA1) subfamily (NHEs, SLC 9) play an important role in many physiological processes, including cell volume regulation, acid–base homeostasis, and ammonia excretion. The soil nematode Caenorhabditis elegans (Maupas, 1900) (N2, 1968) expresses nine paralogues (NHX-1 to NHX-9). The current study was undertaken to investigate the role of the cation/proton exchanger in hypodermal Na+ and H+ fluxes, as well in ammonia excretion processes. Measurements using SIET (scanning ion-selective electrode technique) showed that the hypodermis promotes H+ secretion and Na+ uptake. Inhibitory effects on fluxes were observed upon application of amiloride but not EIPA, suggesting that NHXs are not involved in the transport processes. In response to stress induced by starvation or exposure to 1 mmol·L−1 NH4Cl, pH 5.5, or pH 8.0, body pH stayed fairly constant, with changes in mRNA expression levels detected in intestinal NHX-2 and hypodermal NHX-3. In conclusion, the study suggest that hypodermal apically localized EIPA-sensitive Na+/H+ exchangers do not likely play a role in ammonia excretion and Na+ uptake in the hypodermis of C. elegans, whereas apical amiloride-sensitive Na+ channels seem to be involved not just in hypodermal Na+ uptake but indirectly also in NH4+ and H+ excretion.