Reeves W B, Dudley M A, Mehta P, Andreoli T E
Department of Internal Medicine, University of Texas Medical School, Houston 77225.
Am J Physiol. 1988 Dec;255(6 Pt 2):F1138-44. doi: 10.1152/ajprenal.1988.255.6.F1138.
We evaluated the effects of osmotic gradients on 22Na+ influx in vesicles prepared from rat outer renal medulla. 22Na+ influx driven in a coflow mode by an inwardly directed 100 mM KCl gradient was measured at 20 and 60 s; 1 mM bumetanide inhibited approximately 30% of 22Na+ influx. The bumetanide-sensitive 22Na+ influx was reduced by approximately 65% when either K+ or Cl- was omitted from the aqueous phases. We found that an osmotic gradient for vesicle shrinkage, that is, 600 mM urea in the extravesicular medium, enhanced the bumetanide-sensitive 22Na+ influx twofold. Conversely, an osmotic gradient for vesicle swelling, that is, with vesicles but not extravesicular media loaded with 600 mM urea, produced a 50% suppression of bumetanide-sensitive 22Na+ influx. Moreover, 600 mM extravesicular urea, an osmotic gradient for vesicle shrinkage, also reduced uptake of the nonspecific marker [14C]mannitol. These effects of osmotic gradients were not due to alterations in ionic driving forces, since bumetanide-sensitive 22Na+ influx driven in a counterflow mode by loading the vesicles with 100 mM NaCl also was activated or suppressed by osmotic gradients for vesicle shrinkage or swelling, respectively. We conclude that osmotic gradients, and/or vesicle volume changes, modulate bumetanide-sensitive Na+:K+:2Cl- activity.
我们评估了渗透梯度对从大鼠肾外髓质制备的囊泡中22Na+内流的影响。在20秒和60秒时测量了由内向的100 mM KCl梯度以并流模式驱动的22Na+内流；1 mM布美他尼抑制了约30%的22Na+内流。当水相中省略K+或Cl-时，布美他尼敏感的22Na+内流减少了约65%。我们发现，囊泡收缩的渗透梯度，即囊泡外介质中600 mM尿素，使布美他尼敏感的22Na+内流增加了两倍。相反，囊泡肿胀的渗透梯度，即囊泡中而非囊泡外介质中加载600 mM尿素，使布美他尼敏感的22Na+内流受到50%的抑制。此外，600 mM囊泡外尿素，一种囊泡收缩的渗透梯度，也减少了非特异性标记物[14C]甘露醇的摄取。渗透梯度的这些作用并非由于离子驱动力的改变，因为通过向囊泡中加载100 mM NaCl以逆流模式驱动的布美他尼敏感的22Na+内流也分别被囊泡收缩或肿胀的渗透梯度激活或抑制。我们得出结论，渗透梯度和/或囊泡体积变化调节布美他尼敏感的Na+:K+:2Cl-活性。
