Differentiation of the active sodium transport system during metamorphosis in Rana catesbeiana skin in relation to cadmium- and amiloride-induced responses.

Abstract

The differentiation of the sodium active transport system across Rana catesbeiana skin during metamorphosis was investigated and the system was analyzed by the effects of Cd2+ and amiloride. Active transport of Na in the frog skin first appeared at stage XXI of the tadpole, indicated by the appearance of a potential difference (PD) and a short circuit current (SCC) across the skin. The effects of epidermal application of Cd2+ and amiloride on the various indicators of active Na transport were as follows: (1) Cd2+ increased PD and SCC after stage XXII; (2) Cd2+ also increased the skin resistance (RM) from stage B to XXIII, but decreased it after stage XXV; and (3) amiloride decreased PD and SCC but increased RM after stage XXI. The adult frog skin can be expressed as an equivalent circuit by three parameters : ENa, the electromotive force of the active Na current, and RNa and R~, corresponding to the resistance to the active Na current and the resistance of the shunt pathway, respectively. These three parameters were calculated from the amiloride effect on PD and SCC. ENa was almost null and RNa was infinite until stage XX. ENa then gradually increased, while RNa was fairly constant between 10 and 20 kQ .cm2 after stage XXI. RE gradually increased during metamorphosis. These data suggest that there is not an active Na pathway but a passive one in the early stage of metamorphosis of the tadpole, and that the active Na transport system suddenly appears at stage XXI and gradually develops thereafter.

Active ion transport and morphofunctional organization in the skin of the alpine newt,Triturus alpestrisduring the life cycle

“…In this context, our research is aimed at detecting new morphological characteristics according to the new functional performance of the integument that develops during metamorphosis (Takada, 1985;Galeyeia/., 1987).…”

“…It is now accepted that a trans-epithelial potential (PD) and a «short circuit current» (SCC), e.g. active Na + transport, are present in larval anurans at Taylor-Kollros stage XXI (Taylor & Barker, 1965;Takada, 1985). PD and SCC were observed across the skin of the pedomorphic urodeles Amphiuma means and Siren lacertina (Bentley, 1973;1975), while a low rate of Na + transport across the skin has been reported in pedomorphic Ambystoma tigrinum (Cox, 1986).…”

Glycoconjugate histochemistry of mucous glands in the skin of metamorphosing Bufo viridis

“…It is comprised of two major parts: a mucus-covered epidermis and underlying dermis. During metamorphosis, distinct structural changes occur in the skin paralleled by changes in its functional properties (Takada 1985;Fox 1986), for example, mucous glands develop and dorsal skin of body transforms to adult skin, whereas tail skin disappears by tail resorption at metamorphic climax stage (Kaltenbach et al 2004;Kinoshita et al 2005). Cutaneous mucus produced by intradermal mucous glands protects amphibians from excessive water loss or gain, acts as a barrier that protects from bacterial and fungal infections and minimizes mechanical damage to the skin out of water (Clarke 1997).…”

Prolactin increases open-channel density of epithelial Na+channel in adult frog skin

“…Transcellular active Na + transport across the skin, measured as the amiloride-blockable short-circuit current (SCC), has been identified in a wide variety of anuran and urodelan genera, including Rana, Leptodactylus, Bufo, Cynops and Ambystome species (Bentley and Yorio, 1977;Rabito et al, 1978;Bentley and Baldwin, 1980;Hillyard et al, 1982;Takada, 1985;Takada and Komazaki, 1986;Takada and Hara, 1988). This transport develops during the climax stages of metamorphosis in the bullfrog, and is due to the development of an epithelial Na + channel (ENaC).…”

“…This transport develops during the climax stages of metamorphosis in the bullfrog, and is due to the development of an epithelial Na + channel (ENaC). Therefore, the appearance of transcellular active Na + transport as SCC and/or ENaC is a marker of the development of adult-type features by the skin (Cox and Alvarado, 1979;Hillyard et al, 1982;Takada, 1985).…”