Selective in vivo and in vitro sampling of proteins using miniature ultrafiltration sampling probes

The most widely used in vivo sampling technique, microdialysis sampling, provides important data on the extracellular concentration of low molecular mass (<1000-5000 Da) species. However, biological macromolecules of much greater mass (>20-90 kDa) have key in vivo roles as chemical messengers or are currently under consideration as biopharmaceuticals. Microdialysis, which utilizes a sampling process based upon analyte diffusion, is largely ineffective at monitoring the local, transient extracellular concentrations of important macromolecular species. Ultrafiltration sampling is an in vivo sampling technique utilizing a convective, rather than diffusive, sampling mechanism. This paper demonstrates the effective recovery (>90%) of model proteins with molecular weights up to 68 000 from in vivo and in vitro sites through the use of miniature ultrafiltration sampling probes. Selectivity in the sampling process can be achieved through alteration of the membrane structure. In vivo ultrafiltration sampling in conjunction with slab gel electrophoresis and silver staining detects three recovered proteins (MW 9100-26 800) present in the extracellular space of a series of rats.