| Article details | |||
| Article title |
Phenformin and 5-aminoimidazole-4-carboxamide-1-b-D-ribofuranoside (AICAR) activation of AMP-activated protein kinase inhibits transepithelial Na+ transport across H441 lung cells
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| Author |
Woollhead, A. M. Scott, J. W. Hardie, D. G. Baines, D. L.
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| Journal title |
JOURNAL OF PHYSIOLOGY -LONDON THEN CAMBRIDGE-
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| Bibliographic details | 2005, VOL 566; NUMBER 3, pages 781-792 | ||
| Publisher |
Blackwell Publishing Ltd
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Country of publication | Great Britain |
| ISBN | ISSN | 0022-3751 | |
| Language | English | ||
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Abstract: Active re-absorption of Na+ across the alveolar epithelium is essential to maintain lung fluid balance. Na+ entry at the luminal membrane is predominantly via the amiloride-sensitive Na+ channel (ENaC) down its electrochemical gradient. This gradient is generated and maintained by basolateral Na+ extrusion via Na+,K+-ATPase an energy-dependent process. Several kinases and factors that activate them are known to regulate these processes; however, the role of AMP-activated protein kinase (AMPK) in the lung is unknown. AMPK is an ultra-sensitive cellular energy sensor that monitors energy consumption and down-regulates ATP-consuming processes when activated. The biguanide phenformin has been shown to independently decrease ion transport processes, influence cellular metabolism and activate AM…
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| 5-Aminoimidazole-4-carboxamide riboside (AICAR) enhances GLUT2-dependent jejunal glucose transport: a possible role for AMPK |
| John WALKER*, Humberto B. JIJON*, Hugo DIAZ*, Payam SALEHI†, Thomas CHURCHILL† and Karen L. MADSEN*1 |
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| *Division of Gastroenterology, University of Alberta, 6146 Dentistry Pharmacy Building, Edmonton, Alberta, Canada T6G 2C2, and †Department of Surgery, University of Alberta, Edmonton, Alberta, Canada T6G 2C2
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AMPK (AMP-activated protein kinase) is a key sensor of energy status within the cell. Activated by an increase in the AMP/ATP ratio, AMPK acts to limit cellular energy depletion by down-regulating selective ATP-dependent processes. The purpose of the present study was to determine the role of AMPK in regulating intestinal glucose transport. [3H]3-O-methyl glucose fluxes were measured in murine jejunum in the presence and absence of the AMPK activators AICAR (5-aminoimidazole-4-carboxamide riboside) and metformin and the p38 inhibitor, SB203580. To differentiate between a sodium-coupled (SGLT1) and diffusive (GLUT2) route of entry, fluxes were measured in the presence of the SGLT1 and GLUT2 inhibitors phloridzin and phloretin. Glucose transporter mRNA levels were measured by reverse transcriptase–PCR, and localization by Western blotting. Surface-expressed GLUT2 was assessed by luminal biotinylation. Activation of p38 mitogen-activated protein kinase was analysed by Western blotting. We found that treatment of jejunal tissue with AICAR resulted in enhanced net glucose uptake and was associated with phosphorylation of p38 mitogen-activated protein kinase. Inhibition of p38 abrogated the stimulation of AICAR-stimulated glucose uptake. Phloretin abolished the AICAR-mediated increase in glucose flux, whereas phloridzin had no effect, suggesting the involvement of GLUT2. In addition, AICAR decreased total protein levels of SGLT1, concurrently increasing levels of GLUT2 in the brush-border membrane. The anti-diabetic drug metformin, a known activator of AMPK, also induced the localization of GLUT2 to the luminal surface. We conclude that the activation of AMPK results in an up-regulation of non-energy requiring glucose uptake by GLUT2 and a concurrent down-regulation of sodium-dependent glucose transport.
Key words: 5-aminoimidazole-4-carboxamide riboside (AICAR), AMP-activated protein kinase, glucose, GLUT2, p38, SGLT1.
Abbreviations used: ACC, acetyl-CoA carboxylase; AICAR, 5-aminoimidazole-4-carboxamide riboside; AMPK, AMP-activated protein kinase; BBM, brush-border membrane; MAPK, mitogen-activated protein kinase; mTOR, mammalian target of rapamycin; PD, potential difference; RT, reverse transcriptase.
1To whom correspondence should be addressed (email karen.madsen@ualberta.ca).
Received 27 April 2004/23 August 2004; accepted 15 September 2004
Published as BJ Immediate Publication 15 September 2004, DOI 10.1042/BJ20040694
The Biochemical Society, London ©2005
