Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA106

Poster Communications

The jejunum epithelium adapts quickly to hypoxic insults by modifying transepithelial glucose transport

F. Dengler1, R. Rackwitz1, H. Pfannkuche1, G. Gäbel1

1. Institute of Veterinary Physiology, Leipzig University, Leipzig, Germany.

The gastrointestinal epithelium is known to tolerate huge variations in oxygen supply. Thus, it must command elaborate adaptation mechanisms to maintain its key functions like nutrient uptake. We hypothesized that the import of energy substrates into the intestinal epithelial cells must be tightly regulated under hypoxia and elucidating its adaptation might also shed light on the underlying mechanisms. We incubated isolated lagomorph jejunum epithelia in Ussing chambers under short-circuit-conditions. After equilibration, we simulated hypoxia by gassing a group of epithelia with 1% O2 + 99% N2. We assessed electrogenic transport of glucose and the dipeptide glycyl-glutamine, respectively by measuring the increase of short-circuit current (Isc) after mucosal addition of each substrate. Transepithelial transport of glucose, orthomethyl-glucose (OMG) and mannitol was determined radioactively. Additionally, we incubated the epithelia with inhibitors for different glucose transport mechanisms and evaluated their effect on 14C-glucose transport. After only 45 minutes of hypoxia, a significant decrease in the glucose- and glycyl-glutamine-induced Isc was observed compared to the control group, i.e. a decreased activity of secondary active transport mechanisms. Despite the reduced electrogenic import of glucose, its transepithelial transport was not diminished by hypoxic conditions. Paracellular integrity was kept up as indicated by mannitol flux rates. Effects of (altered) intracellular metabolism on glucose permeation could be excluded by the use of OMG. Thus, the active import by SGLT 1 was presumably supplemented by other transport mechanisms. An inhibition of transepithelial glucose transport by a specific inhibitor of glucose transporter (GLUT) 1 detectable under hypoxic but not under control conditions revealed an involvement of GLUT 1. We assessed the influence of AMP-activated protein kinase (AMPK) by preincubating the epithelia with its antagonist compound C before submitting them to hypoxia. By doing so, we could abolish the decrease in SGLT 1 activity under hypoxia. Western blot studies revealed a phosphorylation, i.e. activation of AMPK under hypoxia that was also abolished by compound C. Summing up, we could show that nutrient transport mechanisms in jejunum epithelium are modulated quickly under hypoxic conditions. A substitution of the energy-dependent import via SGLT 1 by GLUT 1 mediating facilitated diffusion might help to secure an energy-saving uptake of the cells' most important fuel and thus maintaining their function. This adaptation process seems to be mediated by AMPK.

Where applicable, experiments conform with Society ethical requirements