Rapoport J, Abuful A, Chaimovitz C, Noeh Z, Hays R M
Department of Nephrology, Soroka Medical Center, Beersheva, Israel.
Am J Physiol. 1988 Sep;255(3 Pt 2):F429-33. doi: 10.1152/ajprenal.1988.255.3.F429.
Urea is actively transported inwardly (Ji) across the skin of the green toad Bufo viridis. Ji is markedly enhanced in toads adapted to hypertonic saline. We studied urea transport across the skin of Bufo viridis under a variety of experimental conditions, including treatment with amiloride and phloretin, agents that inhibit urea permeability in the bladder of Bufo marinus. Amiloride (10(-4) M) significantly inhibited Ji in both adapted and unadapted animals and was unaffected by removal of sodium from the external medium. Phloretin (10(-4) M) significantly inhibited Ji in adapted animals by 23-46%; there was also a reduction in Ji in unadapted toads at 10(-4) and 5 x 10(-4) M phloretin. A dose-response study revealed that the concentration of phloretin causing half-maximal inhibition (K1/2) was 5 x 10(-4) M for adapted animals. Ji was unaffected by the substitution of sucrose for Ringer solution or by ouabain. We conclude 1) the process of adaptation appears to involve an increase in the number of amiloride- and phloretin-inhibitable urea transport sites in the skin, with a possible increase in the affinity of the sites for phloretin; 2) the adapted skin resembles the Bufo marinus urinary bladder with respect to amiloride and phloretin-inhibitable sites; 3) we confirm earlier observations that Ji is independent of sodium transport.
尿素可通过主动转运（Ji）进入绿蟾蜍（Bufo viridis）的皮肤。在适应高渗盐水的蟾蜍中，Ji显著增强。我们研究了在各种实验条件下尿素通过绿蟾蜍皮肤的转运情况，包括使用氨氯吡脒和根皮素进行处理，这两种药物可抑制海蟾蜍（Bufo marinus）膀胱的尿素通透性。氨氯吡脒（10⁻⁴ M）在适应和未适应的动物中均显著抑制Ji，但不受外部介质中钠去除的影响。根皮素（10⁻⁴ M）在适应的动物中显著抑制Ji达23% - 46%；在未适应的蟾蜍中，10⁻⁴ M和5×10⁻⁴ M的根皮素也使Ji降低。剂量反应研究表明，使适应动物产生半数最大抑制（K1/2）的根皮素浓度为5×10⁻⁴ M。用蔗糖替代林格溶液或用哇巴因处理均不影响Ji。我们得出以下结论：1）适应过程似乎涉及皮肤中可被氨氯吡脒和根皮素抑制的尿素转运位点数量增加，且这些位点对根皮素的亲和力可能增加；2）就可被氨氯吡脒和根皮素抑制的位点而言，适应后的皮肤类似于海蟾蜍的膀胱；3）我们证实了先前的观察结果，即Ji与钠转运无关。
