Propionate transport in rat liver cells.
Propionate extraction by liver is generally in the range of 95%, which could depend on a transport process across the cell membrane. The study reports conditions in which [14C]propionate uptake can be measured with minimal interferences from metabolism. Propionate uptake by isolated hepatocytes was mediated by two components: a low-affinity component of limited physiological interest and a high-affinity (apparent Km about 0.15 mM) component. This last component displayed a high capacity but was not Na+-dependent nor concentrative. Propionate transport was not markedly affected by acetate, butyrate or other C3 glucogenic compounds; it was inhibited by halogenated monocarboxylates, monochloroacetate and 2-chloropropionate being the most potent. Classical inhibitors of anion transport and of functional-SH groups were ineffective. Propionate uptake was responsive to external pH: stimulated by acidic and depressed by alkaline pH. Hepatic uptake of propionate in vivo was practically quantitative up to 0.8-1.0 mM in afferent plasma, in keeping with the measured capacity of the high-affinity component. It is suggested that propionate uptake is essentially carrier mediated but this process should not be rate limiting for hepatic utilization in physiological conditions.
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002264:Carboxylic Acids / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D011422:Propionates / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D002264:Carboxylic Acids; D011422:Propionates; C029658:propionic acid