Ionic gradients within mantle-collar epithelial cells of the land snail Otala lactea

Abstract

Aestivating Otala lactea have been shown to reduce the rate of evaporative water loss from the cells of the mantle-collar epithelium to a level comparable to that of an insect. X-ray microanalyses of ultrathin frozen sections from aestivating and non-aestivating snails have shown gradients of chloride and potassium ions in the apical microvillus region of the regulating mantle collar epithelium. The greatest difference in osmotic concentration occurs in the apical 2 micron of the cell. There appears to be a barrier at that level that prevents water being mobilised from the underlying tissues. Methods of presenting data generated by X-ray microanalysis are also discussed.

Water‐regulatory Behaviour in Terrestrial Gastropods

“…It appears that the reduction in Cook, 1y81 a , ) evaporation from the mantle is actually due to an increase in the concentration of Na+ and K+ in the apical cytoplasm of the epithelial cells (Machin, I 966, I 972, I 974). It has been suggested that these inclusions may be involved in the increase in ionic concentration in the apical cytoplasm (Appleton, Newell & Machin, 1979). In addition it has been found that the cytoplasm of mantle epithelial cells in dormant Otala lactea contained a large concentration of lamellate vesicles and associated microtubules (Newell & Machin, 1976; Appleton & Newell, 1977).…”

“…In addition it has been found that the cytoplasm of mantle epithelial cells in dormant Otala lactea contained a large concentration of lamellate vesicles and associated microtubules (Newell & Machin, 1976; Appleton & Newell, 1977). It has been suggested that these inclusions may be involved in the increase in ionic concentration in the apical cytoplasm (Appleton, Newell & Machin, 1979).…”

Short‐ and long‐term resistance to desiccation in a minute litter‐dwelling land snail Lauria cylindracea (Pulmonata: Pupillidae)

“…One of the most potent mechanisms is the regulation of water evaporation from the mantle (Machin, 1965), probably through the control of water loss by a water proo®ng layer close to the surface of the mantle tissue (Machin, 1974). This was experimentally veri®ed in Otala lactea (Newell & Machin, 1976;Appleton, Newell & Machin, 1979) who showed that in aestivating snails a vascular water barrier was developed in the apical parts of the epithelial cells, where strong osmotic gradients of chloride and potassium are established. These gradients prevent the transfer of water from the underlying tissue.…”

Biology of the Integument

“…Since the mucus is isosmotic to haemolymph, a diffusion gradient between haemolymph and mucus is abolished in favour of a mechanical method of transport of water to the surface. During inactivity, most pulmonate snails withdraw into their shell and it seems that the mantle collar epidermis (which has an extremely low permeability) is responsible for reducing evaporative water loss (Machin 1974, Appleton et al 1979). Without mucus extrusion, the diffusional permeability of the epidermis is unable to sustain normal levels of evaporative water loss.…”