THE DEPENDENCE ON MEMBRANE FLUIDITY OF CALCIUM-OXALATE CRYSTAL ATTACHMENT TO IMCD MEMBRANES

The development of urolithiasis is a multifaceted process, starting wi th urine supersaturation and ending with the formation of mature renal calculi. The retention of microcrystals by kidney tubule epithelium c ell membranes has been proposed as a critical event in the process. To date, attachment of kidney stone constituent crystals to urothelial c ells has been demonstrated both in vitro and in vivo yet the mechanism of crystal attachment remains unknown. We hypothesize that for effect ive stone crystal attachment to the epithelium there must be cell memb rane rearrangement that would allow for long-range bonding between the stone crystal and the cell membrane. This rearrangement may be influe nced by the physical state of the membrane. The current study examines calcium oxalate monohydrate (COM) crystal attachment to inner medulla ry collecting duct (IMCD) cells following changes in cell membrane flu idity. Radioactively labeled COM crystals were used to quantitate crys tal attachment. Membrane fluidity was altered by changing temperature, cell membrane cholesterol content, or extended length of cell culture . Crystal attachment to IMCD cells was directly correlated to changes in membrane fluidity. This finding was consistently observed regardles s of the method used to alter membrane fluidity. The results are consi stent with the theory that the ability to form a crystal attachment re gion on the cell surface may be related to the ease of rearrangement o f membrane components at the cell surface. Variations in the urothelia l cell environment during certain pathological conditions in the kidne y could induce these physical perturbations and prime kidney epithelia l cells at or near the papillary tip to bind COM crystals.