Costanzo L S, Windhager E E
Am J Physiol. 1978 Nov;235(5):F492-506. doi: 10.1152/ajprenal.1978.235.5.F492.
Calcium and sodium transport were studied in the distal convoluted tubule of the rat by micropuncture and microperfusion techniques. The animals received either control infusions, 0.9% saline at 0.02 ml/min, or chlorothiazide (CTZ), 0.5 mg/min-kg. In free-flow micropuncture, distal calcium reabsorption occurred against an electrochemical gradient; it was 9% of the filtered load in the controls and 13.8% in the CTZ-treated rats. The drug dissociated calcium and sodium transport along the distal tubule. Absolute reabsorptive rates for calcium and sodium, measured in pump perfusion experiments, were proportional to the distal loads. CTZ, acting from the lumen, enhanced net calcium (P less than 0.01) and reduced net sodium (P less than 0.01) reabsorption. In stationary microperfusion experiments, sodium backflux produced rapid establishment of a steady-state concentration of 50 mM. In contrast, net backflux of calcium was negligible. With calcium in the luminal perfusion fluid, there was a concentration-dependent reabsorptive efflux which was not saturated at a luminal calcium concentration of 9.5 mM and which was enhanced by CTZ.
采用微穿刺和微灌注技术研究了大鼠远曲小管中的钙和钠转运。给动物分别进行对照输注，以0.02 ml/min的速度输注0.9%生理盐水，或给予氯噻嗪（CTZ），剂量为0.5 mg/min-kg。在自由流微穿刺实验中，远曲小管的钙重吸收是逆电化学梯度进行的；在对照组中，其为滤过负荷的9%，在CTZ处理的大鼠中为13.8%。该药物使远曲小管中的钙和钠转运发生解离。在泵灌注实验中测得的钙和钠的绝对重吸收率与远曲小管负荷成正比。从管腔起作用的CTZ增强了钙的净重吸收（P<0.01），并减少了钠的净重吸收（P<0.01）。在固定微灌注实验中，钠的回流使稳态浓度迅速达到50 mM。相比之下，钙的净回流可忽略不计。当管腔灌注液中有钙时，存在浓度依赖性的重吸收流出，在管腔钙浓度为9.5 mM时未达到饱和，且CTZ可增强这种流出。
