The majority of influenza A viruses isolated from wild birds, but not humans, can replicate in the duck intestinal tract. Here we demonstrate that all duck isolates tested universally retain sialidase activities under low pH conditions independent of their neuraminidase (NA) subtypes. In contrast, the sialidase activities of most isolates from humans and pigs practically disappear below pH 4.5, with the exception of four human pandemic viruses isolated in 1957 and 1968. Sequence comparisons among duck, human, and swine N2 NA subtypes indicate that amino acids at positions 153, 253, 307, 329, 344, 347, 356, 368, 390, and 431 may be associated with the low pH stability of duck and human pandemic N2 NAs. This finding suggests that the low pH stability of duck influenza A virus NA may be a critical factor for replication in the intestinal tract through the digestive tract of ducks, and that the properties of NAs are important for understanding the epidemiology of the influenza virus.
These data indicate that low osmolality is a crucial factor to facilitate water absorption, and the electrolytes, sodium and chloride, can effectively be salvaged in the colon.
Sulfatide, which binds to in£uenza A viruses and prevents the viral infection, was found to inhibit the sialidase activities of in£uenza A viruses in a pH-dependent manner. The kinetic parameters of the e¡ect of sulfatide on the sialidase activities of human in£uenza A viruses using £uorometric assay indicated that sulfatide was a powerful and non-competitive type inhibitor in low-pH conditions. ß
Key wordsoral rehydration solutions, passive water transport, sodium-chloride coupled transport, small intestine, colon.Acute diarrhea, particularly in infants, is a major cause of morbidity across the world. 1 The role of oral rehydration solutions (ORS) in acute diarrhea is to provide water and electrolytes via the gastrointestinal tract as quickly as possible.In the present study, two hypotonic ORS, an isotonic ion solution and distilled water were evaluated by an in vivo perfusion technique with the whole gut of anesthetized rats. 2,3The aim of the present study was to evaluate the regional difference of net water and electrolytes absorption in the gut and further to elucidate the intestinal water and electrolytes absorption mechanisms.
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