NDT Advance Access published online on July 29, 2007
Nephrology Dialysis Transplantation, doi:10.1093/ndt/gfm497
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The cellular contribution to effluent potassium and its relation with free water transport during peritoneal dialysis
1Division of Nephrology, Department of Internal Medicine, Academic Medical Center, University of Amsterdam, 2Dianet Foundation Amsterdam-Utrecht and 3Department of Experimental Hepatology, Academic Medical Center, University of Amsterdam, The Netherlands
Correspondence and offprint requests to: Annemieke Marcella Coester, MD, Academic Medical Center, Department of Internal Medicine, Division of Nephrology, A01-114, PO Box 22700, 1100 DE Amsterdam, The Netherlands. Email: a.m.coester{at}amc.uva.nl
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Abstract |
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Background. Aquaporin-1 (AQP-1) dysfunction is one of the valid theories for decreased free water transport (FWT) in long-term peritoneal dialysis (PD) ultrafiltration failure (UFF). We questioned whether apoptosis of peritoneal cells could be reflected in an increased release of cellular (CR) K+ and explain AQP-1 dysfunction. If so, negative relationships between CR-K+ and FWT would be expected. Therefore, we analysed CR-K+ to total peritoneal K+ removal, for possible relationships with FWT, the duration of PD, the presence of late UFF and effluent cancer antigen (CA) 125.
Methods. Standard peritoneal permeability analyses done with 3.86% glucose were investigated cross-sectionally in three extreme groups: group I: 19 patients <1year on PD; group II: 20 patients >4 years on PD without UFF; group III: 19 patients >4 years on PD with UFF.
Results. Group III had the lowest values of FWT and CR-K+ (P < 0.01). CR-K+ had a positive correlation with FWT in groups I and II, but not in group III. These correlations were also present using much simpler methodologies: replacement of CR-K+ by mass transfer area coefficient (MTAC)-K+/MTAC-creatinine ratio or dialysate over plasma (D/P)-K+/D/P-creatinine ratio and replacement of FWT by Na+-sieving. No relationship with CA125 was present.
Conclusions. This study shows that other than diffusive and convectional, K+ transport is not excluded in patients treated with conventional glucose-based PD solutions. We found evidence for release of K+ from cells. In general, CR-K+ was related to parameters of FWT, except for long-term patients with UFF. This suggests glucose-induced hypertonic cell shrinkage as a basic physiological phenomenon during PD. The absence of this relationship in long-term PD patients with UFF either suggests a reduction or inhibition of K+-channels and may be due to another mechanism than AQP-1 dysfunction. Most likely, CR-K+ in UFF does not reflect apoptosis. However, the D/P-K+/D/P-creatinine ratio may be useful in detecting peritoneal changes.
Keywords: fluid kinetics; peritoneal dialysis; peritoneal transport; potassium; ultrafiltration failure; water channels
Received for publication: 7.12.06
Accepted in revised form: 29. 6.07
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