Doping-induced disappearance of ice II from water’s phase diagram

Water and the many phases of ice display a plethora of complex physical properties and phase relationships 1–4 that are of paramount importance in a range of settings including processes in Earth’s hydrosphere, the geology of icy moons, industry and even the evolution of life. Well-known examples include the unusual behaviour of supercooled water 2 , the emergent ferroelectric ordering in ice films 4 and the fact that the ‘ordinary’ ice Ih floats on water. We report the intriguing observation that ice II, one of the high-pressure phases of ice, disappears in a selective fashion from water’s phase diagram following the addition of small amounts of ammonium fluoride. This finding exposes the strict topologically constrained nature of the ice II hydrogen-bond network, which is not found for the competing phases. In analogy to the behaviour of frustrated magnets 5 , the presence of the exceptional ice II is argued to have a wider impact on water’s phase diagram, potentially explaining its general tendency to display anomalous behaviour. Furthermore, the impurity-induced disappearance of ice II raises the prospect that specific dopants may not only be able to suppress certain phases but also induce the formation of new phases of ice in future studies

Sodium selectivity of semicircular canal duct epithelial cells

<p>Abstract</p> <p>Background</p> <p>Sodium absorption by semicircular canal duct (SCCD) epithelial cells is thought to contribute to the homeostasis of the volume of vestibular endolymph. It was previously shown that the epithelial cells could absorb Na⁺under control of a glucocorticoid hormone (dexamethasone) and the absorptive transepithelial current was blocked by amiloride. The most commonly-observed target of amiloride is the epithelial sodium channel (ENaC), comprised of the three subunits α-, β- and γ-ENaC. However, other cation channels have also been observed to be sensitive in a similar concentration range. The aim of this study was to determine whether SCCD epithelial cells absorb only Na⁺or also K⁺through an amiloride-sensitive pathway. Parasensory K⁺absorption could contribute to regulation of the transduction current through hair cells, as found to occur via vestibular transitional cells [S. H. Kim and D. C. Marcus. Regulation of sodium transport in the inner ear. <it>Hear.Res</it>. doi:10.1016/j.heares.2011.05.003, 2011].</p> <p>Results</p> <p>We determined the molecular and functional expression of candidate cation channels with gene array (GEO GSE6197), whole-cell patch clamp and transepithelial recordings in primary cultures of rat SCCD. α-, β- and γ-ENaC were all previously reported as present. The selectivity of the amiloride-sensitive transepithelial and cell membrane currents was observed in Ussing chamber and whole-cell patch clamp recordings. The cell membrane currents were carried by Na⁺but not K⁺, but the Na⁺selectivity disappeared when the cells were cultured on impermeable supports. Transepithelial currents across SCCD were also carried exclusively by Na⁺.</p> <p>Conclusions</p> <p>These results are consistent with the amiloride-sensitive absorptive flux of SCCD mediated by a highly Na⁺-selective channel, likely αβγ-ENaC. These epithelial cells therefore absorb only Na⁺via the amiloride-sensitive pathway and do not provide a parasensory K⁺efflux from the canals via this pathway. The results further provide caution to the culture of epithelial cells on impermeable surfaces.</p