Osmoregulation and Excretion

Abstract

The article discusses advances in osmoregulation and excretion with emphasis on how multicellular animals in different osmotic environments regulate their milieu intérieur. Mechanisms of energy transformations in animal osmoregulation are dealt with in biophysical terms with respect to water and ion exchange across biological membranes and coupling of ion and water fluxes across epithelia. The discussion of functions is based on a comparative approach analyzing mechanisms that have evolved in different taxonomic groups at biochemical, cellular and tissue levels and their integration in maintaining whole body water and ion homeostasis. The focus is on recent studies of adaptations and newly discovered mechanisms of acclimatization during transitions of animals between different osmotic environments. Special attention is paid to hypotheses about the diversity of cellular organization of osmoregulatory and excretory organs such as glomerular kidneys, antennal glands, Malpighian tubules and insect gut, gills, integument and intestine, with accounts on experimental approaches and methods applied in the studies. It is demonstrated how knowledge in these areas of comparative physiology has expanded considerably during the last two decades, bridging seminal classical works with studies based on new approaches at all levels of anatomical and functional organization. A number of as yet partially unanswered questions are emphasized, some of which are about how water and solute exchange mechanisms at lower levels are integrated for regulating whole body extracellular water volume and ion homeostasis of animals in their natural habitats. © 2014 American Physiological Society.

Hypotonicity Stimulates Potassium Flux through the WNK-SPAK/OSR1 Kinase Cascade and the Ncc69 Sodium-Potassium-2-Chloride Cotransporter in the Drosophila Renal Tubule

“…The Malpighian tubules of insects are renal epithelia that play an essential role in iono-and osmoregulation (3,4). Because the fly tubules are bathed in hemolymph, they can directly sense changes in its osmolarity.…”

“…Insect iono-and osmoregulation is achieved through epithelial ion transport across the midgut, Malpighian (renal) tubules, and hindgut/rectum (3,4). Because the renal tubules are in direct contact with hemolymph (the blood compartment of the insect), they can directly sense changes in extracellular osmolarity.…”

Functional Plasticity of the gut and the Malpighian tubules underlies cold acclimation and mitigates cold-induced hyperkalemia inDrosophila melanogaster

“…Most ion and water reabsorption occurs at 138 specialized areas of thickened rectal epithelia called rectal pads that actively absorb ions to create 139 local osmotic gradients for the reabsorption of water (Larsen et al, 2014). 140…”

“…http://dx.doi.org/10.1101/224832 doi: bioRxiv preprint first posted online Nov. 24, 2017; ensuring exposure of the excised ureter to the paraffin oil where secreted fluid would accumulate 268 to be collected for analysis (see Larsen et al, 2014). 269…”

Recent advances in understanding trans-epithelial acid-base regulation and excretion mechanisms in cephalopods

“…54,105 In vertebrate systems Rh glycoproteins including Rhbg and Rhcg were identified as central players facilitating the export of ammonia (NH 3 ) in concert with proton secretion mechanisms allowing a NH 4 C trapping mechanism in the acidified boundary layer of excretory cells. [106][107][108][109] Just lately Rh proteins were also found and characterized in a range of invertebrates including crustaceans and insects. [110][111][112] Also in cephalopods one Rh-protein (RhP) has been identified, which has the highest degree of identity to RhPs cloned from the decapod crustaceans Carcinus maenas (50%) and Metacarcinus magister (56 %).…”