Solute transport through the bone lacunar-canalicular system is believed to be essential for osteocyte survival and function. We have developed an approach that permits direct measurement of real-time solute movement in intact bones by using fluorescence recovery after phtobleaching (FRAP) technology [1]. The movement of vitally injected fluorescence dye (sodium fluorescein) among individual osteocytic lacunae was visualized in situ and the transport was analyzed by using a two-compartment mathematical model of solute diffusion. Our previous studies [1] suggested that the matrix surrounding osteocytes is similar to the glycocalyx of endothelial cells as first proposed by Weinbaum et al. (1994) [2]. In the present study, we investigated diffusive transport of five fluorescent tracers of different molecular weights and shapes in the bone lacunar-canalicular system (LCS). Our hypothesis is that the solute transport in lacunar-canalicular system is size and shape dependent, due to the molecular sieving of the pericellular matrix.

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