Macromolecule transport across glomerular capillaries: Application of pore theory

Measurements of transport rates of various high-molecular-weight solutes across capillaries have contributed significantly to our understanding of the functional properties of both renal and extrarenal microcirculatory systems [1–7]. In addition to serum albumin and other plasma proteins, nonprotein polymers such as dextran and polyvinylpyrrolidone (PVP) also have been used successfully as transport probes. Complementing these quantitative measurements of macromolecular transport are the more qualitative insights into permeation pathways gained from studies with macro-molecules as ultrastructural tracers [6, 8, 9]. As a result of these investigations, it has become apparent that several factors influence the transcapillary movement of macromolecules, including molecular size, molecular charge, and perhaps even “shape”. In addition, transport rates are known also to be influenced by plasma flow rate and other hemodynamic variables. In an effort to better understand how these various factors combine to govern the transport of macromolecules, several theoretical descriptions of transcapillary exchange have been developed. Much of this work has been based on hydrodynamic models of solute transport through pores, first applied to capillaries by Pappenheimer [4] and Pappenheimer, Renkin, and Borrero [10]. This review will summarize the current status of the pore model, with emphasis on its application to the study of macromolecule transport across glomerular capillaries.