Shpun S, Katz U
Department of Biology, Technion, Haifa, Israel.
Biol Cell. 1989;66(1-2):179-81.
Urea fluxes across the urinary bladder of Bufo viridis were studied in vitro after modification of the mounting technique. The fluxes increased as a function of the bath urea concentration, saturating near 200 mmol/l. The apparent Km was 88 mmol/l in the bladders from tapwater-acclimated toads, and 107 mmol/l in toads acclimated to 500 mOsm NaCl. The Vmax which was 300 mumol.h-1.cm-2 at room temperature in bladders from tapwater acclimation, changed to more than 1500 mumol.h-1.cm-2 upon salt acclimation. It is suggested that urea movement across the urinary bladder of this species occurs by facilitated diffusion and that salt acclimation induces an increase in the density of this pathway, but not of its characteristics (Km).
在改进安装技术后，对绿蟾蜍膀胱的尿素通量进行了体外研究。通量随浴液尿素浓度的增加而增加，在接近200 mmol/l时达到饱和。自来水中适应的蟾蜍膀胱的表观Km为88 mmol/l，而适应500 mOsm NaCl的蟾蜍膀胱的表观Km为107 mmol/l。自来水中适应的蟾蜍膀胱在室温下的Vmax为300 μmol·h-1·cm-2，盐适应后变为超过1500 μmol·h-1·cm-2。有人认为，该物种膀胱中尿素的转运是通过易化扩散进行的，盐适应会导致该途径的密度增加，但其特性（Km）不变。
