著者

長井 孝紀 田中 滋康 高田 真理

出版者

日本膜学会

雑誌

膜 (ISSN:03851036)

巻号頁・発行日

vol.29, no.3, pp.154-160, 2004-05-01 (Released:2011-03-04)

参考文献数

20

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Amphibians regulate the osmotic and ionic composition of their body fluids by water and ion transport across their skin. When dehydrated, desert toads press down the pelvic region of ventral skin on moist surfaces to achieve maximal water absorption. Aquaporins (AQP) are trans-membrane proteins permeable to water. We cloned three isoforms of AQP (AQP-h1, -h2, -h3) in tissues of tree frogs. AQP-h3 was abundantly expressed in the pelvic region of ventral skin, facilitating water absorption across the skin. Antibodies to AQP-h3 labeled the cell membrane of the granulosum cells in the skin. AQP-h3 was progressively expressed during metamorphosis of larval frogs. Expression of AQP-h3 was facilitated by and diuretic hormone, argine vasotocin. Collectively, AQP-h3 is a molecule to play a positive role in water absorption across the amphibian skin. In bullfrogs short circuit current across the skin was suppressed by amiloride, a blocker for epithelial Na+ channel (ENaC), showing that transport of sodium ions occurs through ENaC. Na+ transport increased in parallel with metamorphosis of the tadpole. In cultured skins of the tadpole Na+ transport was facilitated by aldosterone, but counteracted by prolactin. Such counteraction seemed to be removed by thyroid hormone (T3) during metamorphosis to adapt a terrestrial environment.

著者

竹内 浩昭 岡田 洋子 谷津 香織 大庭 つき恵 長井 孝紀

出版者

日本爬虫両棲類学会

雑誌

爬虫両棲類学雑誌 (ISSN:02853191)

巻号頁・発行日

vol.17, no.4, pp.156-163, 1998-12-30 (Released:2009-03-27)

参考文献数

23

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The behavioral responses of axolotls to chemical stimuli representing the four basic taste qualities (sweetness, saltiness, sourness, and bitterness) were quantified by measuring the ratio of rejection and the number of bites of gel pellets that contained various concentrations of sucrose, NaCl, citric acid, or quinine hydrochloride. A simplified method to measure the hardness of gel (gel strength) was devised and the feeding responses towards various hardnesses of gel pellets were also quantified by measuring the rejection ratios. Rejection ratios towards chemical stimuli other than sweet gels tended to increase with concentration and the degree of rejection was different depending on the quality of taste. These results showed good correspondence to those of a previous study, suggesting that axolotls distinguish the salty, sour, and bitter tastes, but not sweet tastes. The number of bites was dependent on the concentrations as well as the taste qualities, and bites on sour and bitter gels showed a different type of biphasic concentration dependency. When the hardness of gel pellets was changed at a constant concentration of chemical stimuli, the rejection ratios tended to increase with gel strength. The potential of salty taste to induce swallowing (a preference for salty taste) was suggested by reductions in the rejection ratios when gel pellets included NaCl but not sucrose.