THE PERMEABILITY OF INDIVIDUALLY PERFUSED FROG MESENTERIC CAPILLARIES TO T1824 AND T1824‐ALBUMIN AS EVIDENCE FOR A LARGE PORE SYSTEM

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Abstract
Landis [1963, 1964] perfused single capillaries of the frog mesentery with Ringer solutions containing T1824 and bovine albumin, and observed spots of dye outside the vessels within a few seconds. He suggested these localized regions of high permeability might represent the large pores which have been proposed to account for the permeability of normal capillaries to large protein molecules. Binding curves of T1824 to bovine albumin reported in the present paper (which confirm the results of others) suggest that 50% of the T1824 in the perfusates used by Landis was in an unbound state. The free diffusion coefficients of T1824 and T1824‐albumin complex have been measured and found to be 1·64 10‐6 cm2 sec‐1 for T1824 and 0·59 10‐6 cm2 sec‐1 for T1824‐albumin complex. Stokes‐Einstein radii calculated from the free diffusion coefficients are 1·31 nm for T1824 and 3·62 nm for T1824‐albumin complex; thus unbound T1824 may be regarded as a small molecule.When individual capillaries of frog mesentery were perfused via a micropipette with Ringer solution containing T1824 and no albumin, dye escaped from the vessels within the first 30 sec in twenty‐six out of thirty‐one perfusions. When capillaries were perfused with solutions containing T1824‐albumin complex and no unbound dye, no dye left the capillaries during the first 30 sec in forty‐three out of forty‐seven perfusions.In thirteen experiments in which the same capillary was perfused separately with Ringer solutions containing T1824‐albumin complex and no free dye, and with T1824 and no albumin, dye crossed the capillary walls during the first 30 sec of perfusion only when free dye was present. In seven experiments the rate of passage of T1824 was compared when the same vessel was perfused with T1824 and a solution of T1824‐albumin complex and an excess of unbound T1824. These experiments indicate that T1824‐albumin complex slows the movement of T1824 across the capillary wall.Since the rapid movement of dye out of capillaries is seen only when perfusates contain unbound T1824, it is concluded that Landis's observations indicate non‐uniform permeability to small molecules and may not be used as evidence for a large pore system.

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