David Porcel

Alterations in the digestive gland and shell of the snail Helix aspersa Müller (gastropoda, pulmonata) after prolonged starvation

We investigated the effects of prolonged starvation on body weight and shell thickness, on the numbers of different types of cells, and on the Mg/Ca ratio in the digestive gland and shell in the common garden snail Helix mprsa Miiller. A 60% reduction in body weight, which occurred after periods of starvation longer than 3 months, was critical for life. Starvation had a marked effect on the relative numbers of cells in the digestive gland, and significantly decreased the number of digestive cells. The changes in Mg/Ca ratio in the digestive gland and shell were closely correlated. Changes in ion balance may have resulted from the need to compensate for the starvation-induced decline in extracellular pH. The shell acted as a reservoir of ions that could be mobilized under extreme conditions. COMP BIOCHEM PHYSIOL 115A;l:ll-17, 1996.

Phosphatase activity in the hepatopancreas of Helix aspersa

1. Phosphatase acid (PhA) activity in the digestive gland (hepatopancreas) of the common garden snail Helix aspersa has been investigated using cytochemical methods. 2. All the cells composing this gland show PhA activity, the distribution pattern differing according to the cell type. 3. The digestive cells show the most widely distributed reaction product (brush border, phagolysosomes, multivesicular bodies and autophagic vacuoles). 4. In the excretory cells this activity appears in large sacs, while in the calcium cells the reaction product is abundant in the calcium granules. 5. Cellular digestion processes performed by each of these cell types is discussed together with their role in the detoxification of heavy elements derived from the environment.

Expanding Forces in Aqueous Outflow Pathways of a Nonaccommodating Mammal: An Approach via Comparative Dynamic Morphology

Six dog eyes were fixed by intracameral perfusion of fixative at pressures of 0, 5, 10, 15, 20, and 25 cm of water. Eight dog eyes were fixed after the injection in both ocular chambers of a number of cholinergic agents, either singly or in combination. Under the effect of miotics and under increased ocular pressure, the aqueous pathways expand. An analysis of the forces involved in expansion of the exit pathways reveals the primary role of the detached ciliary body in nonaccommodating mammals. Two mechanisms appear to have been conserved in dogs and humans throughout evolution. The first is an active mechanism: the opening of the trabecular meshwork as a consequence of the combined action of the ciliary muscle and the iris and its insertion ligaments-the uveoscleral trabeculate-in dogs, and the longitudinal portion of the ciliary muscle and scleral spur in humans. The second is a passive mechanism: the infundibular arrangement of the drainage structures assisted by the traction on the zonular ligament of the lens, which responds to an increase in pressure in the anterior chamber by widening the pathways, thus favoring outflow.

A structural and microanalytical (EDX) study of calcium granules in the hepatopancreas of Helix aspersa

Abstract 1. 1. The garden snail Helix aspersa has a large number of calcium cells in its digestive gland, or hepatopancreas. 2. 2. These cells contain a large amount of membrane-bound intracellular granules which are the sites of accumulation of a wide variety of cations and which also act as a mechanism of deposition and liberation of these ions. 3. 3. These granules also act as a detoxification mechanism for a variety of heavy-metal ions contained in the snails diet. 4. 4. This study concentrates on the analysis of these granules using transmission and scanning electron microscopy and X-ray microanalysis (EDX). 5. 5. The granules are surrounded by a membrane and contain deposits of material arranged in concentric layers around a condensation nucleus. 6. 6. The most important components of these deposits of inorganic material are calcium, phosphorus and magnesium. 7. 7. There is speculation about the possible origin of these granules and their role in a great number of physiological processes, such as the regulation of the luminal pH of the intestine, regenerative processes of the shell, cell death, and detoxification mechanisms of heavy metals.

Cell-Cell Adhesion in the Prelaminar Region of the Optic Nerve Head: A Possible Target for Ionic Stress

Purpose: This paper aims to study the anterior surface of the optic nerve in relation to its ability to support a source of stress acting from the vitreous cavity. The intercellular junctions of the lining astrocytes mediated by cellular adhesion molecules (CAMs) may be the main targets for ionic stress. Methods: The optic nerve of the domestic pig was prepared for light, confocal laser and transmission electron microscopy. Immunostaining was performed for antibodies against glial fibrillary acidic protein, neural cadherin (N-cadherin) and neural CAM (N-CAM). Results: Only 1 type of intercellular junction was found among the bordering astrocytes, which was characterized as a zonula adherens. Unions between lining cells showed a positive immunogold effect and immunofluorescence against N-cadherin in the zonula adherens and membrane apposition. N-CAM was also present in areas of nonjunctional cellular adhesion. Conclusion: The stability of intercellular junctions of the nerve-vitreous boundary is sensitive to altered concentrations of Ca2+. Since aqueous humor has half the Ca2+ concentration of plasma, any contact of aqueous humor with the optic nerve head can interfere with the ionic concentration of calcium in the extracellular spaces. This mechanism may contribute to age-related changes and some types of glaucoma.

Mapping the surface astrocytes of the optic disc: a fluid‐conducting role of the astrocytic covering of the central vessels

Background:  The vitreous interface of the optic nerve has been studied to delimit the covering of Elschnigs astrocytes and interstitial pathways of flow through the prelaminar region.

Expression of Metabolic Coupling and Adhesion Proteins in the Porcine Optic-Nerve Head: Relevance to a Flow Model of Glaucoma

Francisco-Javier Carreras1, David Porcel2, Francisco Rodriguez-Hurtado3, Antonio Zarzuelo4, Ignacio Carreras1 and Milagros Galisteo4 1Department of Surgery (Ophthalmology), Faculty of Medicine, University of Granada 2Center of Scientific Instrumentation, University of Granada, 3Division of Ophthalmology, Licinio de la Fuente University Hospital, Granada, 4Department of Pharmacology, Faculty of Pharmacy, University of Granada, Spain

Fenestrations and preferential flow routes in the prelaminar optic nerve through wet scanning electron microscope and perfusion of tracers

Purpose:  We study the vitreous interface of the optic disc to delimit the passages for the flow of fluids through the prelaminar tissue of porcine eyes.

Chondroitin Sulfate Is a Major Proteoglycan Constituent of Human Cameral Mucous Gel

The presence of chondroitin- and heparan sulfate-containing proteoglycans and type IV collagen was searched for in human cameral mucous gel (CMG). Monoclonal antibodies specific for human heparan sulfate, chondroitin sulfate and collagen IV were used in ultrathin sections of Lowicryl-embedded human CMG. Only chondroitin sulfate is revealed with this method. Heparan sulfate and collagen IV were not elicited by the monoclonal antibodies. We conclude that chondroitin sulfate is a major component of the proteoglycans of human CMG, where it may contribute to the colloidosmotic properties of the gel and play a role in the outflow of aqueous humor.

Characterization of Glycoconjugates in the Human Cameral Mucous Gel by Lectins

A cameral mucous gel (CMG) has been described in human eyes lining the anterior and posterior ocular chambers. We assay a battery of 11 lectins to characterize the accessible sugars of the presumed glycoproteins and glycosaminoglycans present in the gel. Results show a predominance of alpha-linked sugars over beta-linked ones. There is evidence for the prominence in the gel of alpha-N-acetyl-D-galactosamine and/or alpha-D-galactose, together with alpha-N-acetyl-glucosamine. The second most important sugars are beta-N-acetyl-D-glucosamine and the dissacharide beta-D-galactose-N-acetyl-D-galactosamine. beta-N-acetyl-galactosamine could possibly be identified in third place. Neither fucose nor mannose are detected. These results point towards heparan and perlecan as possible components of the glycidic fraction of the gel, although a specific proteoglycan adapted to the osmotic role of the CMG is not at all unlikely.