Adaptation of low-phosphate diet in renal brush borders of spontaneously hypertensive rats

A LPD seems to increase the Pi uptake by vesicles of the BBM of the renal cortex. This study was done to find if there was adaptation to a LPD in the BBM vesicles from the superficial or deep cortex in SHR, with WKY rats as control. The fractional excretion of Pi of SHR on the LPD was higher than that of WKY rats (p less than 0.01). The Vmax of Pi uptake in BBM vesicles from superficial cortex of WKY rats on the LPD was greater (p less than 0.05) than in such rats on a diet with a normal level of phosphate. Thus, the adaptation to a LPD was normal in WKY rats. However, in BBM vesicles from the superficial cortex of SHR kidneys, the difference in this Vmax depending on diet was insignificant. In BBM vesicles of the deep cortex of SHR kidneys, this Vmax was higher (p less than 0.01) on the LPD. The apparent Km was not significantly different in different groups or parts of the renal cortex. These results suggest that BBM vesicles in the superficial cortex of SHR kidneys did not adapt to the LPD. The less adaptation in SHR in vivo indicates that there may be a defect in Pi transport in BBM vesicles of the superficial cortex of SHR kidneys.