The Present State of the Carrier Hypothesis

Oleate uptake by cardiac myocytes is carrier mediated and involves a 40-kD plasma membrane fatty acid binding protein similar to that in liver, adipose tissue, and gut.

“…1), virtually abolished the effilux of the labeled species. Furthermore, as expected (27), [3H]oleate efflux rates under these conditions were trans-stimulated by increasing extracellular concentrations of unbound, unlabeled oleate (Fig. 4 B (14), adipocytes (12,20), and jejunal enterocytes (13).…”

“…Moreover, it is increasingly apparent that saturable uptake is a necessary but not sufficient criterion to establish that a transport process is carrier mediated (24). In the current report we demonstrate that myocyte oleate uptake also displays countertransport and trans-stimulation, two other important features of carrier-mediated transport (27,28). Countertransport is typically established by demonstrating cellular effilux of labeled compound against the prevailing concentration gradient upon addition of unlabeled compound to the incubation mixture (27 negligible.…”

“…In the current report we demonstrate that myocyte oleate uptake also displays countertransport and trans-stimulation, two other important features of carrier-mediated transport (27,28). Countertransport is typically established by demonstrating cellular effilux of labeled compound against the prevailing concentration gradient upon addition of unlabeled compound to the incubation mixture (27 negligible. Under these circumstances it would be possible to follow the effilux of the internalized label from the cell by measurements ofcellular radioactivity.…”

Drug transporters in pharmacokinetics

“…Xenobiotics are by definition compounds which are not essential for the maintenance of a physiological function; they may, however, modulate, ameliorate or damage such functions, depending on whether they are drugs, diagnostics, or toxins. Living organisms, therefore, have also developed processes to eliminate "non-physiological" xenobiotics by carrier mediated transport (LeFevre 1975). This article focuses mainly on transporter-based elimination of drugs by the liver.…”

Glucose movement into rat uterine fluid

“…Phloretin, which is an inhibitor of the facilitated transport of glucose in red cells and other systems (Le Fevre & Marshall, 1959), was added to the luminal fluid at a concentration of 10~4 m after 30 min, but had no significant effect on the rate of glucose appearance. Sugars which share the same transport system as glucose can influence glucose fluxes, either by competition or by inducing the phenomenon of countertransport (Le Fevre, 1975). However, neither galactose nor 3-O-methyl-D-glucose added to the lumen at a concentration of 10 mM after 30 min had a significant effect on the rate of glucose apperance.…”