Can hypoosmotic shock and calcium influx lead to translocation of aquaporin-1 in shrimp muscle cells?

The physiological variations during the crustacean molting cycle have intrigued researchers for many years. Maintaining osmotic homeostasis in the face of hemolymph dilution and dealing with dynamic intracellular and extracellular calcium fluctuations are challenges these animals continuously confront. It has recently been shown that water channels present in the cell membrane (aquaporins) are essential for water uptake during premolt and postmolt. This study aims to investigate whether hypoosmotic shock and intracellular and extracellular calcium variations can lead to translocation of Aquaporin 1 (AQP-1) from the intracellular region to the plasma membrane during premolt and postmolt, thus allowing increased water flow in these stages. For this, we investigate in vitro the rapid change of AQP-1 positions in the abdominal muscle cells in the freshwater shrimp, Palaemon argentinus. Using cell volume analysis and immunohistochemistry, we show that hypoosmotic conditions and an elevation of the intracellular and extracellular calcium concentrations are concurrent with the translocation of AQP-1 to the plasma membrane. These results indicate that calcium flux and hypoosmotic shock may be regulators of AQP 1 in the translocation process.

The effects of vesicle toxin from the sea anemone Bunodosoma cangicum on the behavior of a freshwater shrimp, Palaemon argentinus, and shore crab, Neohelice granulata.

Sea anemones of the genus Bunodosoma possess along their body column, longitudinally arranged brown-colored vesicles. We have shown that in B. cangicum, these warty structures contain a mixture of potent toxins. This work highlights the neuro-inhibitory effects exhibited by two decapod crustacean species exposed to the extracts from these vesicles. For this, we use the unrefined toxin in doses, exposure times, and different exposure pathways. The findings show that at least one neuro-inhibitory compound is present and remains active regardless of the exposure method or dose tested. This toxin affects neuro-motor pathways but not neuro-sensory pathways. Shrimp exposed to toxin could continue to perceive and track food pellets but could not secure and consume their ration. Of six anatomical reflexes tested under the toxin's influence, voluntary movements of the mouthparts were impacted most commonly. Interestingly, all subject animals recovered from the toxin exposure within 2 h. Finally, we propose Reflexive Action Analysis (RAMP) as a tool to evaluate the potency of other neurotoxic or neuro-inhibitory compounds in crustacea. This work is the first to show the neuro-inhibitory activity of extracts from these sea anemone columnar vesicle structures and the first to evaluate these effects using RAMP reflex analysis.

Participation of Na+/K+-ATPase and aquaporins in the uptake of water during moult processes in the shrimp Palaemon argentinus (Nobili, 1901).

Due to the presence of the exoskeleton, the moult cycle is a required event in the life of crustaceans. In order for the exoskeleton to be replaced, it is necessary for these animals to uptake water from the environment for their body tissues during the late pre-moult, ecdysis and in the early post-moult for the expansion of the new cuticle. The mechanisms and organs used to uptake water in these events are not yet completely clear. In this study, we investigated the participation of aquaporins and Na+/K+-ATPase in cells of two potential organs responsible for the uptake of water (gills and gut) at three different stages of the moult cycle in freshwater shrimp Palaemon argentinus. We showed the participation of these two proteins with different functional patterns in gills and intestinal cells as water uptake pathways for moult and early post-moult. Our results indicate that Na+/K+-ATPase promotes the necessary osmotic gradient in the gills for water uptake through the gut cells during the pre-moult. This process, in turn, remains active during the post-moult stage with the addition of water influx through the gill cells.

Aquaporin in different moult stages of a freshwater decapod crustacean: Expression and participation in muscle hydration control.

Crustaceans, during their moult cycle, at the stages of both pre-moult and post-moult, need water uptake. This movement of water creates a challenge for the regulation of cell volume. The cells of freshwater decapods require a high regulatory capacity to deal with hyposmotic stresses, given the need to face dilution of the haemolymph during their moult cycles. This study investigated the variation in the expression of water channels (aquaporins) along the moult cycle of a freshwater palaemonid shrimp, focusing on their role in cell volume regulation. Moults in Palaemonetes argentinus have been investigated along three stages of its moult cycle: intermoult, late pre-moult and recent post-moult. For the evaluation of tissue volume regulation, the weight of isolatedmuscle, subjected to isosmotic and hyposmotic salines, was followed for 60min. The expression of AQP during the different moult stages was evaluated by immunocytochemistry. Muscle from the three moult stages in isosmotic conditions showed the same pattern of tissue volume regulation. When muscle from animals in pre-moult and intermoult were submitted to hyposmotic stress they swell, followed by volume regulation, while in post-moult the regulation is compromised. The difference in volume regulatory control between pre-moult and post-moult may be related to a possible regulation of water channels, as AQP expression was equal at these stages. This study presents novel findings for crustaceans in general, in the demonstration that AQP expression changes during the moult cycle of a decapod crustacean, together with the regulation of cell volume with the participation of AQPs.