H+, Na+, K+, and amino acid transport in caterpillar and larval mosquito alimentary canal

William R. Harvey*, Bernard A. Okech

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

5 Scopus citations


Two principal strategies are used to energize membranes in living organisms, a Na+ strategy and a voltage strategy. In the Na+ strategy a primary Na+/K+ ATPase imposes both Na+ and K+ concentration gradients across cell membranes with Na+ high outside and K+ high inside the cells. The Na+ gradient, Δ[Na+] is used to drive diverse secondary transporters. For example, in many animal cells Δ[Na+] drives Na+ inwardly coupled to H+ outwardly, mediated by Na+/H+ exchangers (NHEs). They provide the principal means by which metabolically produced acids are ejected from mammalian cells [70]. In the voltage strategy the electron transport system of prokaryotes or H+ V-ATPases of eukaryotes, impose a voltage gradient, ΔΨ, across biological membranes with the outside positive. The ΔΨ drives secondary (Na+ or K+)/nH+ antiport that is mediated by Na+/H+ antiporters (NHAs). The stoichiometry of NHEs is 1Na+ to 1H+ so they are independent of the membrane potential and are said to be electroneutral. The stoichiometry of NHAs is 1Na+ or K+ to more than 1H+ so they are driven both by the ion gradients and the membrane potential and are said to be electrophoretic. NHAs operate in the opposite direction from NHEs, moving nH+ inwardly and Na+ or K+ outwardly. ΔΨ also drives Na+- or K+-coupled nutrient amino acid uptake that is mediated by electrophoretic (Na+ or K+) amino acid symporters (NATs) [11]. In eukaryotic cells the primary sources of voltage gradients across plasma membranes have classically been considered to be K+, Na+, or other ionic diffusion potentials. Thus, K+ diffusion potentials dominate the resting potential and Na+ diffusion potentials dominate the action potential in squid axon and many other nerves. Only recently are ΔΨs generated by H+ V-ATPases becoming recognized as the energy source for electrophoretic transporters in animal cells [35, 65, 90]. The H+ V-ATPases translocate H+ outwardly across the cell membrane leaving their partner anion (gegenion) behind. Thus, they charge the capacitance of the membrane resulting in a transmembrane voltage, with the outside positive. The translocated H+s exchange with more numerous Na+s or K+s in the outside bulk solution, transforming the H+ electrochemical gradient to a Na+ or K+ electrochemical gradient which in turn drives Na+- or K+-coupled amino acid symport via a NAT into the cells. Membrane energization by H+ V-ATPases is accomplished by a five-phase system consisting of (1) the bulk solution inside the cells, (2) the inside solution/membrane interface, (3) the membrane, (4) the outside solution/membrane interface, and (5) the outside bulk solution [36, 49, 50]. The chapter is divided into five parts: (1) voltage-driven transporters and their terminology, (2) a summary of progress from the concept of active K+ transport through the discovery of portasomes and their role in the isolation of the so-called K+ pump to the cloning of its component H+ V-ATPase and K+/2H+ antiporter, (3) the cloning and localization of components of the H+ V-ATPase-Na+/H+ antiporter-NAT system of mosquito larval alimentary canal (AC), with emphasis on the cloning of the first, putatively electrophoretic, Na+/nH+ antiporter from Anopheles gambiae (AgNHA1), (4) attempts to characterize NHEs and NHAs heterologously in Xenopus oocytes, and (5) the incorporation of existing data into a qualitative model of the mosquito system for taking up amino acids while recycling H+, Na+, and K+ between lumen, cells, and hemolymph as well as generating longitudinal pH gradients in the absence of barriers along the AC of mosquito larvae.

Original languageEnglish
Title of host publicationEpithelial Transport Physiology
PublisherHumana Press Inc.
Number of pages36
ISBN (Electronic)9781603272292
ISBN (Print)9781603272285
StatePublished - 2010
Externally publishedYes


  • African malaria mosquito
  • Anopheles gambiae
  • NHA
  • NHE
  • NHE
  • Xenopus laevis oocytes
  • pH


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