CCKB/gastrin receptors mediate changes in sodium and potassium absorption in the isolated perfused rat kidney

Background To evaluate the function of cholecystokinin B (CCKB)/gastrin rec eptors in the rat kidney, we identified the receptors by Northern blot and localized the receptors by immunohistochemistry. The functional effects of gastrin were studied under standardized in vitro conditions using the isola ted perfused kidney. Methods. Rat kidneys were mounted in an organ bath by attaching the renal a rtery to a perfusion system. A catheter was inserted into the renal vein an d the ureter to collect samples that were analyzed for the concentrations o f electrolytes. After a preperfusion period, gastrin-17-I was given via the renal artery (10(-8) to 10(-6) mol/L). Subsequently, hemodynamic parameter s (for example, perfusate flow) and changes in sodium and potassium absorpt ion were determined. All data were subjected to a nonparametric analysis of variance and, in case of significant results, to subsequent paired compari sons by the a posteriori Wilcoxon test. Results. Northern blot analysis detected CCKB receptor transcripts in total RNA isolated from kidneys. Immunohistochemistry localized CCKB receptors o n tubules and collecting duct cells. Compared with controls, gastrin (10(-6 ) mol/L) caused a decrease in the fractional sodium reabsorption (basal 80% , 10 minutes after application of gastrin 71%, after 20 minutes 62%, P < 0. 05). This effect was inhibited by the CCKB receptor antagonist L-365,260. G astrin decreased urinary potassium excretion at 10(-8) and 10(-6) mol/L [ma ximal decrease at 10(-6) mol/L from baseline values (100%) to 49% after 10 minutes and to 69% after 20 minutes, P < 0.05, N = 6]. This effect was also abolished by the CCKB receptor antagonist L-365,260. Gastrin (10(-6) mol/L ) reduced perfusate flow by 31% (P < 0.05). Conclusions. CCKB receptors are expressed in the rat kidney on tubules and collecting ducts. These receptors mediate changes in renal potassium and so dium absorption. Tn addition, gastrin causes a decrease in perfusate how, i ndicating that CCKB receptors might also modulate vascular resistance in th e kidney.