THE EFFECTS OF OUABAIN AND POTASSIUM ON PERITONEAL-FLUID AND SOLUTE TRANSPORT CHARACTERISTICS

Background:We reported anomalous transport characteristics of potassiu m during experimental peritoneal dialysis in rats and suggested that m echanisms of peritoneal potassium transport could be other than simple passive transport. Intracellular transport of potassium in cultured h uman mesothelial cells was reported to be regulated by three different pathways, such as channels blocked by ouabain, channels blocked by fu rosemide, and other. Objective:To investigate the effect of ouabain on peritoneal potassium and water transport characteristics. Methods: A single 4-hour peritoneal dwell was performed in 28 Sprague-Dawley rats . To minimize the diffusive transport of potassium, 4.5 mmol/L of KCl was added into conventional dialysis solution with 3.86% glucose [acid ic peritoneal dialysis solution (APD)]. To evaluate the effect of the pH of dialysis solution on the transport of potassium and water, 4 mmo l/L of NaOH was added into the potassium-containing study solutions [n eutral peritoneal dialysis solution (NPD)]. To evaluate the effect of a potassium channel blocker on peritoneal potassium transport ATPase s ensitive Na+-K+-transport inhibitor, ouabain (10(-5) mmol/L) was added to dialysis solutions immediately before the dwell study in eight rat s with APD (APD-O) and six rats with NPD (NPD-O). Ouabain was not adde d in eight and six rats with APD and NPD (APD-C and NPD-C, respectivel y). They were used as control. Infusion volume was 30 mL. The intraper itoneal volume (V-D) was estimated by using a volume marker dilution m ethod with corrections for the elimination of volume marker, radioiodi nated human serum albumin (RISA), from the peritoneal cavity (K-E). Th e diffusive mass transport coefficient (K-BD) and sieving coefficient (S) were estimated using the modified Babb-Randerson-Farrell model. Re sults: V-D was significantly higher (p < 0.05 from 90 min to 240 min) and K-E (0.027 +/- 0.018 mL/min for APD-O, 0.026 +/- 0.017 mL/min for NPD-O, and 0.030 +/- 0.022 mL/min for NPD-C, vs 0.058 +/- 0.030 mL/min for APD-C, p < 0.05 for each) significantly lower during dialysis wit h APD-O, NPD-O, and NPD-C than with APD-C. The intraperitoneal glucose expressed as a percentage of the initial amount was significantly hig her with APD-O, NPD-C, and NPD-O than with APD-C (p < 0.05 from 90 min to 240 min). K-BD for sodium was higher during dialysis with ouabain than without ouabain, while K-BD for urea, glucose, and potassium, and S for urea, glucose, sodium, and potassium did not differ between the four groups. Conclusions:The physiologic potassium concentration in n eutral dialysis solutions and the use of ouabain decreased the intrape ritoneal fluid absorption. The diffusive transport coefficient and sie ving coefficient for potassium did not differ, while the diffusive tra nsport coefficient for sodium increased during use of ouabain.