We investigated a portable bioartificial renal tubule device (BRTD) consisting of renal tubule cells and hollow fibers, to improve the quality of life of patients. It is necessary for a BRTD system to be compact. A compact portable BRTB requires transfection of an appropriate water channel or electrical pump genes in tubular epithelial cells, which should be based on physiological similarities to human kidney function. LLC-PK(1) cells, into which rat kidney aquaporin 1 (AQP1) cDNA was stably transfected, were evaluated for water transport ability. The expression and localization of water AQP1 were examined by Western blotting, RT-PCR, and immunofluorescence. To measure transcellular water permeation, a simple method was applied, using phenol red as a cell-impermeant marker of concentration. In contrast to wild-type LLC-PK(1) cells, rat AQP1-transfected cells had high transcellular osmotic water permeability. The expression of rat AQP1 mRNA (ratio of AQP1 to beta-actin mRNA) and protein bands (a 28-kDa band and a broad, 35- to 45-kDa band) was confirmed to be stably maintained until a population doubling level of 24. In AQP1-transfected LLCPK(1) cells, the protein was localized mainly to the basolateral side, but also the apical side, of the plasma membrane. Wild-type LLC-PK(1) cells were not stained at the plasma membrane. It is possible that enough AQP1-transfected tubule epithelial cells were supplied for a bioartificial renal tubule device.

The function of current hemodialysis as an artificial kidney is insufficient because of the lack of reabsorptive function. In this study, we intend to develop a bioartificial renal tubule cell device (RTD) using tubular epithelial cells and artificial membranes and to evaluate the reabsorptive function of the confluent layers. Madin-Darby canine kidney (MDCK) cells were cultured on a nucleopore polycarbonate membrane for up to 4 weeks after confluence to examine the influence of the culture period on their ability to transport Na+ actively using Na+/K+ATPase (NKA). The results were (1) active Na+ transport of the cells averaged 24.8 mM/m(2) x 24 h during the initial 2 weeks after confluence and then decreased to about 4.2 mM/m(2) x 24 h during the next 2 weeks; (2) NKA localized on the basal-lateral sides of the cells during the initial 2 weeks, whereas it also localized on the apical side of the cells during the next 2 weeks; (3) long-term culture resulted in an increased number of upheaving cell mass, increased fatty droplets in the cells, and necrosis; and (4) scanning electron microscopy showed fewer microvilli 3-four weeks after confluence. It is concluded that the culture period is critical for developing RTD using cultured renal tubular epithelial cells.

We intend to develop a bioartificial kidney using tubular epithelial cells and artificial membranes, and to evaluate the reabsorptive function of the confluent layers. Madin-Darby canine kidney (MDCK) cells were cultured on a nucleopore polycarbonate membrane for up to 4 weeks after confluence to examine the influence of culture period on their properties, such as the localization of Na+/K+-ATPase and active Na + transport. The results were as follows. Ouabain-sensitive Na + active transport declined at 3 to 4 weeks after confluence in each matrix. The localization of Na+/K+-ATPase indicated depolarization in the cell membrane 3 to 4 weeks after confluence. Prolongation of the culture period increased the formation of an upheaving cell mass after the formation of the confluent monolayer. Scanning electron microscopy revealed fewer microvilli and more flat cells after 3 to 4 weeks of confluency. We conclude that the decline of Na + active transport in the MDCK cells was due to both the formation of multilayers and a decline of cell function throughout the long period of culture following the formation of the confluent monolayers. Further study for selection of membrane material, the extracellular matrix, and species of cells should be continued.

It is difficult for conventional hemodialysis to remove albumin‐binding uremic toxins (ABUTs) even though they are low molecular weight substances. We investigated the efficiency of albumin‐dialysate (AD) for removal of ABUT. Phenols and indoxyl sulfate were selected as ABUT. In vitro dialysis was performed for 2 h in the closed circuit with ABUT containing plasma as a test solution using conventional dialysate (CD) or AD. By the use of CD, the ABUT concentration in the test solution only was reduced by 20 to 30%. On the other hand, AD caused a marked reduction and an increase in test solution and dialysate concentration of ABUT, respectively. ABUT in AD could be adsorbed effectively by activated‐charcoal column; accordingly, the ABUT concentration in the test solution continued to decrease throughout the study period. These results suggest that AD could remove ABUT more efficiently than CD, and AD may be useful for reducing accumulated ABUT levels.

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