Structure, function and translational relevance of aquaporin dual water and ion channels

Abstract

Aquaporins have been assumed to be selective for water alone, and aquaglyceroporins are accepted as carrying water and small uncharged solutes including glycerol. This review presents an expanded view of aquaporins as channels with more complex mechanisms of regulation and diverse repertoires of substrate permeabilities than were originally appreciated in the early establishment of the field. The role of aquaporins as dual water and gated ion channels is likely to have physiological and potentially translational relevance, and can be evaluated with newly developed molecular and pharmacological tools. Ion channel activity has been shown for Aquaporins -0, -1, and -6, Drosphila Big Brain, and plant Nodulin-26. Although the concept of ion channel function in aquaporins remains controversial, research advances are beginning to define not only the ion channel function but also the detailed molecular mechanisms that govern and mediate the multifunctional capabilities. With regard to physiological relevance, the adaptive benefit of expression of ion channel activity in aquaporins, implied by amino acid sequence conservation of the ion channel gating domains, suggests they provide more than water or glycerol and solute transport. Dual ion and water channels are of interest for understanding the modulation of transmembrane fluid gradients, volume regulation, and possible signal transduction in tissues expressing classes of aquaporins that have the dual function capability. Other aquaporin classes might be found in future work to have ion channel activities, pending identification of the possible signaling pathways that could govern activation.

Transcriptional and Microscopic Analyses of Citrus Stem and Root Responses to Candidatus Liberibacter asiaticus Infection

“…L. asiaticus infection repressed expression of genes encoding the pore-forming aquaporins PIP1A, PIP1-1, PIP1-3 while induced expression of SIP1A gene, that belong to the MIP gene family, in the stems (Table 5), where the long distance movement of substances is common. Aquaporins are important molecules in plant physiology because they facilitate the transportation of water and other small, uncharged solutes, such as glycerol, CO2, ammonia and urea, from sources, such as roots and leaves, through the stem to other plant parts [66]–[68]. Their repression in citrus by Ca .…”

Liver-specificAquaporin 11knockout mice show rapid vacuolization of the rough endoplasmic reticulum in periportal hepatocytes after amino acid feeding

“…However, we cannot rule out the possibility that the lack of detectable enrichment in any small metabolite in the AQP11-deficient livers resulted from use of an unsuitable solvent for the extraction or masking of the altered osmolyte by substances isolated from perivenous hepatocytes. Alternatively, the osmotically active substances are inorganic ions rather than small organic osmolytes, as several aquaporins were shown to be capable of ion transport (29).…”

Fundamental structural and functional properties of Aquaporin ion channels found across the kingdoms of life

“…The concept of ion channel activity in an aquaporin has been most comprehensively studied in mammalian AQP1 in terms of structure‐function relationships, pharmacology, and physiological relevance. The number of AQPs designated as aquaporin ion channels is likely continue to increase as the originally disputed concept gains acceptance and lines of evidence accumulate . Ongoing research is addressing the roles of AQP1 and other ion channels in key health challenges such as cancer metastasis and brain oedema.…”