The effect of sodium on p-aminohippurate (PAH) transport kinetics was studied in isolated rat kidney slices in an attempt to define the role of sodium ion in renal organic acid transport. 1. In normally metabolizing renal slices, Na+ increased the Vmax of PAH influx without changing the Michaelis constant (Km). On the other hand, the effIux of preaccumulated PAH was reduced as the Na+ concentration increased. 2. In metabolically impaired renal slices, Na+ had no apparent effect on the influx and efflux of PAH. These results may indicate that Na+ is important for the energy transducing reaction in the PAH transport process.
Aminohippuric Acids/metabolism* ; Animal ; Biological Transport, Active/drug effects ; Culture Media ; Female ; In Vitro ; Kidney/metabolism* ; Kinetics ; Male ; Organ Culture ; Rats ; Sodium/pharmacology* ; p-Aminohippuric Acid/metabolism*

Renal Na+, K+-activated adenosinetriphosphatase (Na-K-ATPase) activity and the p-aminohippurate (PAH) transport kinetics were studied in uninephrectomized rats and cold exposed hamsters. In rats, the specific activity of renal Na-K-ATPase increased by approximately 50% in one week after uninephrectomy and remained more or less constant during the next three weeks. The capacity (Jmax) of PAH influx into the renal cortical slice was sharply increased in one week after nephrectomy, but after which it returned to the control level. In cold exposed hamsters, the specific activity of renal Na-K-ATPase did not increase until 48 days of cold exposure at which time it reached approximately 50% above the control level. On the other hand, the Jmax of PAH influx increased by about 80% in 10 days of co1d exposure and somewhat declined thereafter. These results suggest that PAH active transport in the renal slice is not ratelimited by the activity of Na-K-ATPase under physiological conditions.
Aminohippuric Acids/metabolism* ; Animal ; Biological Transport, Active ; Female ; Hamsters ; Hibernation ; Kidney/enzymology* ; Male ; Na(+)-K(+)-Exchanging ATPase/metabolism* ; Nephrectomy ; Rats ; p-Aminohippuric Acid/metabolism*

This study was undertaken to determine whether verapamil protects renal function in rabbits with ischemic acute renal failure. Renal ischemia was induced by clamping bilateral renal arteries for 60 min. One group received intravenously an infusion of verapamil (lmg/kg) for 30 min prior to initiation of renal artery clamping and the other group received equal volume of saline. Renal blood flow was measured with flowmeter before (basal) and 24 hr after ischemia. Serum creatinine level increased 24 hr after ischemia and remained high to 72 hr. When verapamil was pretreated, the level 48 and 72 hr after ischemia was significantly decreased compared with saline insusion. Urine flow was markedly decreased 24 hr after ischemia and remained depressed to 72 hr, but it was significantly increased 72 hr after ischemia in verapa- mil-pretreatment animals as compared with the saline-infusion animals. GFR were markedly reduced 24 hr after ischemia and remained depressed to 72 hr, which was significantly prevented by verapamil pretreatment. Ischemia caused a significant increase in FEVa and a reduction in Uosm, and TcH2O, indicating impairment in urine concentrating ability of tubules, and the impairment was significantly attenuated by verapamil. The uptake of p-aminohippurate in cortical slices was depressed by ischemia, which was significantly prevented by verapamil pretreatment. In salineinfusion animals, renal blood flow was not significantly different between the basal value and that after 24 hr of reflow. Renal blood flow was not significantly altered by verapamil pretreatment. Anoxia/reoxygenation injury in the control renal slices was not significantly prevented by Ca channel blockers. These results suggest that verapamil exerts a protective effect in ichemic acute renal failure, and the beneficial effects may be attributed to effects other than vasodilation. These data also indicate that a reduction in GFR following ischemia does not result from change in renal blood flow.
Acute Kidney Injury* ; Animals ; Constriction ; Creatinine ; Flowmeters ; Ischemia ; Kidney Concentrating Ability ; p-Aminohippuric Acid ; Rabbits* ; Renal Artery ; Renal Circulation ; Vasodilation ; Verapamil*

The organic anion transporters (OAT) have recently been identified. Although the some transport properties of OATs in the kidney have been verified, the regulatory mechanisms for OAT's functions are still not fully understood. The rat OAT1 (rOAT1) transports a number of negatively charged organic compounds between the cells and their extracellular milieu. Caveolin (Cav) also plays a role in membrane transport. Therefore, we investigated the protein-protein interactions between rOAT1 and caveolin-2. In the rat kidney, the expressions of rOAT1 mRNA and protein were observed in both the cortex and the outer medulla. With respect to Cav-2, the expressions of mRNA and protein were observed in all portions of the kidney (cortex < outer medulla = inner medulla). The results of Western blot analysis using the isolated caveolae-enriched membrane fractions or the immunoprecipitates by respective antibodies from the rat kidney showed that rOAT1 and Cav-2 co-localized in the same fractions and they formed complexes each other. These results were confirmed by performing confocal microscopy with immunocytochemistry using the primary cultured renal proximal tubular cells. When the synthesized cRNA of rOAT1 along with the antisense oligodeoxynucleotides of Xenopus Cav-2 were co-injected into Xenopus oocytes, the [14C]p-aminohippurate and [3H]methotrexate uptake was slightly, but significantly decreased. The similar results were also observed in rOAT1 over-expressed Chinese hamster ovary cells. These findings suggest that rOAT1 and caveolin-2 are co-expressed in the plasma membrane and rOAT1's function for organic compound transport is upregulated by Cav-2 in the normal physiological condition.
Animals ; Biological Transport, Active/*physiology ; CHO Cells ; Caveolins/*metabolism ; Cell Membrane/*metabolism ; Cells, Cultured ; Hamsters ; Immunoprecipitation ; Kidney Tubules, Proximal/*metabolism ; Methotrexate/metabolism ; Microscopy, Confocal ; Oligonucleotides, Antisense/pharmacology ; Oocytes/metabolism ; Organic Anion Transport Protein 1/antagonists & inhibitors/genetics/*metabolism ; RNA, Complementary/metabolism ; RNA, Messenger/genetics/metabolism ; Rats ; Research Support, Non-U.S. Gov't ; Xenopus laevis/metabolism ; p-Aminohippuric Acid/metabolism