Larval bullfrog skin expresses ENaC despite having no amiloride-blockable transepithelial Na⁺ transport

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• 作者：Makoto Takada ; Tomoko Shimomura ; Shigeru Hokari ; Philip J. Jensik and Thomas C. Cox
• 关键词：Frog skin ; Metamorphosis ; ENaC ; Aldosterone ; Prolactin
• 刊名：Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology
• 出版年：2006
• 出版时间：May 2006
• 年：2006
• 卷：176
• 期：4
• 页码：287-293
• 全文大小：371 KB

文摘

Amiloride-blockable Na+ transport, measured as an amiloride-blockable short-circuit current (Am-SCC), is mediated by the epithelial Na+ channel (ENaC). Am-SCC is not normally present in bullfrog tadpole skin, but when such skin is cultured with corticoids an amiloride-blockable Na transport appears. Prolactin (PRL) inhibits its corticoid-induced development. Using specific PCR primers for adult frog ENaC and RT-PCR, we investigated whether corticoids can induce all three ENaC subunits, and whether this expression of ENaC subunit(s) can be blocked by adding PRL with the corticoids. We found that (1) the sequences of the RT-PCR products obtained using primers for α-ENaC were identical between larval and adult skins, (2) the mRNAs for all three ENaC subunits were expressed in larval skin under normal conditions despite no amiloride-blockable Na+ transport being detectable, (3) all three subunits were expressed in larval skins whether they were cultured with corticoids (amiloride-blockable Na transport present) or with corticoids supplemented with PRL (no amiloride-blockable Na transport present). An antibody against a peptide from the α-ENaC of adult bullfrog was localized to the apical cells of both larval and adult skins. Since no amiloride-blockable Na transport exists across larval skin under these conditions, these results suggest that ENaC protein was expressed prior to the onset of transport. ENaC may be in the plasma membrane in an inactivated form or, alternatively, within vesicles waiting to be inserted.