Electron microscopical and histochemical studies of differentiation and function of the cephalopod gill (Sepia officinalis L.)

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

“…alkaline phosphatase, acid phosphatase, carbonic anhydrase, Mg 2C -triphosphatase, b-glucuronidase, glucose-6-phosphate dehydrogenase, malate dehydrogenase, succino-dehydrogenase, monoamine oxidase) indicating active transport processes, whereas the thin outer epithelium, is believed to mainly serve respiratory processes. 39,57 These observations suggest that similar to the situation in fish and crustaceans, the cephalopod gill covers multiple functions including gas exchange, acid-base regulation and ammonia excretion.…”

“…Donaubauer identified the ultrastructural morphology of cephalopod excretory organs, including renal appendages, branchial hearts and gills. 38,39,44 Further studies by Potts and colleagues 40 identified and characterized the gill as major site of NH 4 C excretion in cephalopods. These pioneer studies mainly focused on the physiology of adults leaving a large knowledge gap for early life stages.…”

“…37 Most studies addressing ion regulation and excretion in cephalopods are from the 70 ties and 80 ties focusing on the exploration of nitrogen excretion pathways in these ammonotelic molluscs. [38][39][40][41][42][43] Important studies by R. Schipp and H.H. Donaubauer identified the ultrastructural morphology of cephalopod excretory organs, including renal appendages, branchial hearts and gills.…”

“…71,72 Although the existence of the NKA located in branchial epithelia of the cuttlefish Sepia officinalis was revealed using enzymatic assays in the late 70 ties, its role in branchial ion regulation was less well understood. 39 Molecular characterization of the cephalopod NKA using full length clones of the squid (Loligo opalescens and L. pealeii) NKA revealed fundamental structural differences between osmo-conformers like cephalopods and vertebrates that are capable of maintaining hypo-osmotic conditions in marine environments. 73 The comparatively high Na C concentrations in extracellular fluids of squids (450 mM) compared to lower (100-150 mM) blood Na C concentrations in vertebrates have led to a modification in the charge of amino acids located in the ring at the "external mouth" of the NKA.…”

“…The gills are in direct contact with the water stream inside the mantle cavity, and were suggested to represent important organs mediating the elimination of nitrogenous (NH 4 C ) wastes. 38,39,53,54 The blood is pumped through the gills with the aid of the branchial hearts, contractile blood vessels and muscular movements of the gills. 53,55,56 Inside the gill, the blood enters the primary (1 ) afferent vessel bringing deoxygenated blood to the gill which is then sent to the secondary (2 ) afferent vessel which is located inside the first order (1 ) lamellae and finally distributed to the 3 afferent vessels located in the 2 lamellae.…”