Increased calcium oxalate monohydrate crystal binding to injured renal tubular epithelial cells in culture

The retention of crystals in the kidney is considered to be a crucial step in the development of a renal stone. This study demonstrates the time-dependent alterations in the extent of calcium oxalate (CaOx) monohydrate (COM) crystal binding to Madin-Darby canine kidney (MDCK) cells during their growth to confluence and during the healing of wounds made in confluent monolayers. As determined by radiolabeled COM crystal binding studies and confirmed by confocal-scanning laser microscopy, relatively large amounts of crystals (10.4 ± 0.4 μg/cm ) bound to subconfluent cultures that still exhibited a low transepithelial electrical resistance (TER < 400 Ω ⋅ cm ). The development of junctional integrity, indicated by a high resistance (TER > 1,500 Ω ⋅ cm ), was followed by a decrease of the crystal binding capacity to almost undetectable low levels (0.13 ± 0.03 μg/cm ). Epithelial injury resulted in increased crystal adherence. The highest level of crystal binding was observed 2 days postinjury when the wounds were already morphologically closed but TER was still low. Confocal images showed that during the repair process, crystals selectively adhered to migrating cells at the wound border and to stacked cells at sites were the wounds were closed. After the barrier integrity was restored, crystal binding decreased again to the same low levels as in undamaged controls. These results indicate that, whereas functional MDCK monolayers are largely protected against COM crystal adherence, epithelial injury and the subsequent process of wound healing lead to increased crystal binding.