Frog skin epithelium: Electrolyte transport and chytridiomycosis

Abstract

One unique physiological characteristic of frogs is that their main route for intake of water is across the skin. In these animals, the skin acts in concert with the kidney and urinary bladder to maintain electrolyte homeostasis. Water absorption across the skin is driven by the osmotic gradient that develops as a consequence of solute transport. Our recent study demonstrated that chytridiomycosis, an infection of amphibian skin by the fungal pathogen, Batrachochytrium dendrobatidis, inhibits epithelial Na+ channels, attenuating Na+ absorption through the skin. In frogs that become severely affected by this fungus, systemic depletion of Na+, K+ and Cl− is thought to cause deterioration of cardiac electrical function, leading to cardiac arrest. Here we review the ion transport mechanisms of frog skin, and discuss the effect of chytridiomycosis on these mechanisms.

Endemic Asian Chytrid Strain Infection in Threatened and Endemic Anurans of the Northern Western Ghats, India

“…The fungus colonizes on the keratinous epidermal layers of amphibian skin and affects the exchange of gaseous substances and osmotic balance [16,17]. Bd is known to have affected more than 500 species of amphibians globally [15], and has probably resulted in the decline in the population of more than 200 species of amphibians across the globe [18,19].…”

Role of organic osmolytes in water homoeostasis in skin

“…In certain amphibians, the kidney and the skin function together in maintaining water balance . For example, in frog skin, the steroid hormone aldosterone, normally associated with regulating Na + reabsorption in the kidney , plays an important role in enhancing epidermal reabsorption of sodium chloride and water from the external environment, enabling frogs to adapt to both terrestrial and aquatic environments .…”

Clinical Approach to Dermatologic Disease in Exotic Animals

“…6,7 Amphibian epidermis is typically thin; keratinized; and consists of the stratum corneum, stratum granulosum, stratum spinosum, and the stratum basale. [7][8][9][10][11] Modifications of amphibian skin include the presence of dermal scales (caecilians); folds and grooves for increased surface area (salamanders); partial ossification of the cranial skin and adherence to the skull (bufonids); a specialized highly vascularized ventral dermal organ for water absorption ("drinking patch" in anurans); and the presence of dermal bones (some anurans). 10,12 The stratum corneum is typically shed in one piece at regular intervals and consumed (dermatophagy) unless the animal is ill. 6,11,13 The skin of anurans is loosely adhered to the body and can become edematous in disease states.…”

“…11 Two key features separate adult caecilians and anurans from their larval form: the epidermis is keratinized in adults and the dermis contains a variety of dermal glands. 7,9,11 Mucus, produced by mucous glands and epithelial cells, aids in respiration, prevents evaporative water loss, contains antibacterial and antifungal properties, can be defensive noxious or contain toxic chemicals, may act as pheromones, and can aid in reproduction. 12,[14][15][16][17]…”