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Gen Comp Endocrinol
2011 Dec 01;1743:301-8. doi: 10.1016/j.ygcen.2011.09.007.
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Integument structure and function in juvenile Xenopus laevis with disrupted thyroid balance.
Carvalho ES
,
Fuentes J
,
Power DM
.
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The skin is the largest organ in the body and is a barrier between the internal and external environment. The present study evaluates how PTU, a goitrogen, that is used to treat hyperthyroidism affects the structure and electrical properties of the frog (Xenopus laevis) skin. The results are considered in the context of the two-membrane model established in the seminal work of Ussing and collegues in the 1940s and 1950s. In vitro experiments with skin from Xenopus adults revealed that PTU can act directly on skin and causes a significant increase (p<0.05, One-way ANOVA) in short circuit current (Isc) via an amiloride-insensitive mechanism. Juvenile Xenopus exposed to waterborne PTU (5 mg/L) had a significantly bigger and more active thyroid gland (p<0.01, Student's t-test) than control Xenopus. The bioelectric properties of skin taken from Xenopus juveniles treated with PTU in vivo had a lower Isc, (3.05±0.4, n=13) and Rt (288.2±39.5) than skin from control Xenopus (Isc, 4.19±1.14, n=14; Rt, 343.3±43.3). A histological assessment of skin from PTU treated Xenopus juveniles revealed the epidermis was significantly thicker (p<0.01, Student's t-test) and had a greater number of modified exocrine glands (p<0.01, Student's t-test) in the dermis compared to control skin. Modifications in skin structure are presumably the basis for its changed bioelectric properties and the study highlights a site of action for environmental chemicals which has been largely neglected.
Fig. 1. Short circuit current (Isc, μA/cm2) and tissue resistance (Rt, Ω cm2) in adult Xenopus laevis skin measured in Ussing chambers under voltage clamp (V = 0 mV) in response to increasing levels of PTU applied either to the apical or basolateral side of the preparation. Each column represents the average + SEM of four individuals (basolateral application) or two individuals (apical application). Asterisks represent significant differences from control periods (p < 0.05, One-way ANOVA).
Fig. 2. Short circuit current (Isc, μA/cm2) and tissue resistance (Rt, Ω cm2) in adult Xenopus laevis skin as measured in Ussing chambers under voltage clamp (V = 0 mV). All measurements were performed with amiloride (100 μM) in the apical chamber. After the addition of increasing doses of PTU to the basolateral side, 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB 200 μM) was added to the apical side of the preparation. Panel A – shows a representative electrophysiology trace used to determine the Isc and resistance of adult Xenopus laevis skin. Note that the upward vertical current deflections in the original trace results from a 2 mV pulse of 3 s applied every minute. The amplitude of the deflection was used to calculate change in tissue resistance (ΔI) and the bottom solid line in the original trace represents the Isc. Panel B and Panel C show the Isc and change in resistance respectively, of adult Xenopus laevis skin exposed to increasing doses of PTU on the basolateral side. Each column represents the average + SEM of five individuals. Asterisks represent significant (p < 0.05, One-way ANOVA) differences from the control period (amiloride).
Fig. 3. Sections of the thyroid gland of Xenopus laevis juveniles in control (plate A) and in PTU exposed (5 mg/L) animals (plate B). The right-hand images are higher power amplifications of thyrocytes from control (A’) and PTU (B’) exposed animals. Note the vacuolated appearance of thyrocytes from Xenopus laevis exposed to PTU. (C) Variation in the size of the follicular lumen area and thyrocyte cell height in juvenile Xenopus laevis from control animals and those exposed to PTU (5 mg/L). Each column represents the average ± SEM of six individuals. Asterisks represent significant differences from the control (p < 0.01, Student’s t-test).
Fig. 4. Masson trichrome stained sections of skin from control (A) and PTU exposed (5 mg/L, B) Xenopus laevis juveniles. (C) Graph showing the mean ± SEM (n = 6) of the thickness of the epidermal and dermal layers, respectively, from control and PTU (5 mg/L) treated Xenopus laevis juveniles. Asterisks represent groups which differ significantly from the control (p < 0.01, Student’s t-test).
