Paracellular channel characterized by non-electrolyte permeation through the colonic membrane of the rat.
The mucosa-to-serosa permeability of non-electrolytes through the stripped colonic rat mucosa was examined in a Ussing-type chamber. The permeation clearances for inulin (12-15 A radius) to erythritol (3.2 A radius) increased linearly with the increase in their free diffusion coefficients. On the other hand, the clearances of glycerol, thiourea and urea of less than 3 A radius increased in excess of what would be expected considering the above linearity. This suggests that there are large pores that do not restrict diffusive flow and small pores of 3 A radius or greater that restricted diffusion in the paracellular channel. The transcellular permeation also occurred in a tracer efflux experiment with urea preloaded in colonic stripped mucosa. It was not ruled out that the higher permeability of the nonelectrolytes less than 3 A in radius was due to a transcellular route in parallel with the paracellular one.
Sawada
T
T
Department of Biopharmaceutics, Tokyo College of Pharmacy, Japan.
Tomita
M
M
Hayashi
M
M
Awazu
S
S
D000438:Alcohols / Q000493:pharmacokinetics; D000818:Animals; D003106:Colon / Q000378:metabolism; D004058:Diffusion; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000502:physiology*; D007413:Intestinal Mucosa / Q000378:metabolism*; D008297:Male; D008970:Molecular Weight; D010539:Permeability; D051381:Rats; D011919:Rats, Inbred Strains; D013890:Thiourea / Q000493:pharmacokinetics; D014508:Urea / Q000493:pharmacokinetics
D000438:Alcohols; D014508:Urea; D013890:Thiourea