Characteristics of the chicken proximal cecum hexose transport system |
| |
Authors: | Ruth Ferrer Juana M. Planas Miquel Moretó |
| |
Affiliation: | (1) Departament de Fisiologia Animal, Facultat de Farmàcia, Universitat de Barcelona, Av. Diagonal s/n, E-08028 Barcelona, Spain |
| |
Abstract: | The properties of the sugar transport system present in chicken proximal cecum have been studied and compared to the jejunal transport system. Experiments were carried out in isolated enterocytes from 5- to 7-weak-old birds. Results show that: (1) Cecal cells are capable of high sugar transport rates by a phloridzin-sensitive mechanism. After 60 min incubation, the accumulation ratio (control/phloridzin-incubated cells) for 0.1 mmol/l -methyl-d-glucoside (-MG) was 43 and that of 3-oxy-methyl-d-glucose (3-OMG) was 25. In jejunal cells, ratios were 37 for -MG and 13 for 3-OMG. The differences found in cumulative capacity of 3-OMG between cecal and jejunal cells suggest that the sodium-independent pathway offers a very small contribution to sugar efflux in the steady-state in the former cells. (2) Lowering external Na+ concentration reduces the steady-state -MG accumulation in cecal cells (as in jejunal cells), indicating that the transport system is Na+-dependent. (3) The process depends on the electrochemical Na+ gradient across the cell membrane since both 2,4-dinitrophenol (0.2 mmol/l) and ouabain (0.25 mmol/l) abolish sugar accumulation. (4) Addition of 10 mmol/l 3-OMG to the incubation medium markedly reduces the uptake of -MG (concentration: 0.1 mmol/l), indicating that the cecal transport system can be inhibited by analogues of the transported substrate. (5) The specific sugar transport process is a saturable function of -MG concentration, the apparentKm being 1.02 mmol/l andVm 10.7 nmol/mg cell protein · min. Kinetic constants in jejunal enterocytes were 1.58 mmol/l (Km) and 24.7 nmol/mg cell protein · min (Vm), respectively. In brief, the proximal cecal epithelium has a sugar transport system with properties similar to those of the jejunum which suggests a role of this epithelium in the absorption of hexoses of either ileal or cecal origin. |
| |
Keywords: | Hexose accumulation Proximal cecum Jejunum Isolated enterocytes Chicken |
本文献已被 SpringerLink 等数据库收录! |
|