Attachment sites for particles in the urinary tract

The adherence of crystals to the surface of renal tubule epithelial cells i s one of the initial events in the development of nephrolithiasis. The accu mulation of crystalline material in the kidney will sooner or later result in the formation of a stone. Calcium crystals occasionally are present in t he urine of even healthy individuals, and mechanisms responsible for the se lective attachment of crystals to the tubular epithelium of scene-fanning i ndividuals must exist. Although several types of cell surface molecules, in cluding phosphatidylserine (PS) and sialic acid, have been proposed as rece ptors for crystals in the tubular system, the exact nature of these crystal -binding sites has not yet been revealed. Previously, it was demonstrated t hat calcium oxalate monohydrate crystals adhere to subconfluent, but not to confluent, Madin-Darby canine kidney-I cultures. This model was used here to investigate whether the surface of cells with affinity for crystals is r iched with one of the proposed crystal-binding molecules. Annexin V was use d for the detection of PS at the cell surface, and Sambucus nigra lectin wa s used to reveal terminal sialic acid in a (alpha 2,6) linkage to galactose units. FITC-annexin V binding studies showed that PS was not exposed at th e surface of proliferating or growth-inhibited cells, unless they were pret reated with an apoptosis-inducing cytotoxic agent. Sambucus nigra lectin bi nding, of which the specificity was confirmed by blocking with N-acetylneur aminyl-lactose, demonstrated the abundant presence of (alpha 2,6)-linked si alic acid residues at the cell surface of both subconfluent and confluent c ultures. While these results seem to rule out a role for PS in the adherenc e of calcium oxalate monohydrate crystals to the surface of maturating Madi n-Darby canine kidney-I cells, they question the role for cell surface-asso ciated sialylated glycoconjugates in this process.