Structure, ultrastructure, and immunolocalization of Na+, K+-ATPase, and Na+- K+-2Cl--cotransporter in the compound eye of European lobster, Homarus gammarus:In nearly hatched stage

Among marine invertebrates, compound eyes only attain prominence in a crustacean. The European lobster, Homarus gammarus, is widely distributed throughout the coastal Atlantic waters of northwest Europe, from the Mediterranean Sea to the coast of Norway. Histological studies showed that Homarus gammarus embryo (in nearly hatched stage) compound eye composed of the cornea, crystalline cones, photoreceptor cells, rhabdom and pigmented glial cells. For this study, Adults H. gammarus (ready for spawning) caught off the coast of Brittany and obtained from a shellfish retailer (Les Viviers de Roscoff, Roscoff, France) were maintained at the Montpellier laboratory in natural seawater. The Specimens immersed into Bouin’s fixative, transversal and longitudinal sections of 3 μm were cut and stained with Haematoxylin-Fushin. Immunolocalization of Na+, K+-ATPase was performed through immunofluorescence light microscopy using a mouse monoclonal antibody, IgGα5 and antibody (T4) against NKCC was raised against human colonic NKCC. Electron microscopic examination of compound eye showed each ommatidium contains 8 photoreceptors and their plasma membrane is organized into distinct domains. The distribution of Na+, K+-ATPase, and Na+, K+, 2Cl- cotransporter (NKCC) over this domain was examined by the immunohistochemical study. Immunofluorescence of photoreceptors revealed that distribution of Na+, K+-ATPase, and Na+, K+, 2Cl- co-transporter are restricted to the non-receptive membrane. Whereas no Na+, K+-ATPase and Na+, K+, 2Cl- co-transporter were detected on the light-sensitive microvillar membrane and other sites of ommatidia. These results suggest that despite Homarus gammarus larvae hatched in seawater the distribution of Na+, K+-ATPase and Na+, K+, 2Cl- cotransporter in its compound eye was similar to other terrestrial species that have compound eyes.

Keywords:

Compound eye , European lobster , Homarus gammarus , Na+ , K+-ATPase , Na+-K+-2Cl- co-transporter