Aquaporin 2: Identification and analysis of expression in calves’ urine during their first month of life

Abstract

Michałek, K., Dratwa-Chałupnik, A., Ciechanowicz, A. K. and Malinowski, E. 2014. Aquaporin 2: Identification and analysis of expression in calves’ urine during their first month of life. Can. J. Anim. Sci. 94: 653–659. Aquaporin 2 (AQP2) is a vasopressin-regulated water channel of the renal collecting duct and is excreted into urine. Renal excretion of AQP2 has been studied in humans, dogs, rats and mice. The aim of this study was to identify and analyze expression of AQP2 in calves’ urine. Short and controlled diarrhea was induced in the calves in order to determine any change in renal excretion of AQP2 and to evaluate a possible role of this channel in water balance during the neonatal period. For this purpose, an additional portion of lactose was administered to the calves with a milk replacer. The present work shows that after transient diarrhea associated with excessive supply of lactose in the diet, a significant increase in renal AQP2 excretion was reported in the first 3 wk of the calves’ lives. Renal excretion of this protein in the urine increased significantly despite the absence of changes in the concentration of vasopressin or the osmotic pressure of the blood plasma. The increase observed in the expression of the protein might be associated with the reduction of the total Ca2+ concentration in the blood plasma of calves. The results clearly indicate a different mechanism regulating urinary excretion of AQP2 in newborn calves, hitherto unknown. Although elevated renal excretion of AQP2 was observed, there was no increase in the osmolality of the urine in the calves tested.

Release of urinary aquaporin-2-bearing extracellular vesicles is decreased in pregnant Japanese Black cattle

“…* P <0.05. shows the results of immunoblot analysis for uEV-AQP2. As reported previously for AQP2 in bovine samples [17], both glycosylated and non-glycosylated AQP2 were detected in the uEVs of cattle. Quantitative analysis showed that the levels of glycosylated, non-glycosylated and glycosylated + non-glycosylated (total) AQP2 were significantly decreased in the G group relative to the other two groups.…”

Cellular localization and putative role of aquaporin-2 Ser-261 in the bovine kidney

“…The apparent, exclusive accumulation of AQP2 Ser-261 in the apical plasma membrane observed in the tested calves allowed assuming that this protein, phosphorylated at this position, is most likely primarily involved in water transport to the interior of principal cells and is removed to urine by exocytosis. This could partially explain the increase in renal AQP2 excretion in calves observed in our previous studies with a simultaneous lack of the increase in blood plasma AVP concentration (Michałek et al, 2014a). As mentioned before, AVP-dependent increase in cAMP production and PKA activation are the main factors responsible for the phosphorylation of AQP2 at serine position 256.…”

“…In the absence of AVP stimulation, hypertonicity alone induced rapid plasma membrane AQP2 accumulation in rat kidney CCT (Hasler et al, 2008). Perhaps it is MAPK activation that is the main source of increased AQP2 accumulation in the apical membrane and its total excretion with urine in calves in response to additional water loss with faeces under osmotic diarrhoea (Michałek et al, 2014a). MAPK activation, which probably plays a significant role in the bovine kidney signalling cascade, may also explain the presence of AQP2 Ser-261 in the apical plasma membrane.…”

“…However, the mechanisms regulating renal excretion of this protein, especially during the postnatal period, seem to be slightly different in humans and laboratory animals. In fact, the observed increase in AQP2 excretion in calves in response to additional water losses along with faeces in the course of diarrhoea was not accompanied by a typical increase in plasma vasopressin (AVP) concentration (Michałek et al, 2014a).…”