Glucose transport in the strenuously contracting diaphragm

Rationale: Inspiratory Resistive Breathing (IRB) is an experimental model of increased workload for the respiratory muscles. Contraction of peripheral skeletal muscles leads to muscle glycogen depletion and a compensatory increase in glucose transport possibly through a AMPK-dependent pathway that facilitates GLUT4 translocation to plasma membrane. Objectives: To examine the pathways that regulate glucose transport to the diaphragm during IRB. Methods: Anesthetized, tracheostomized, spontaneously breathing rats were subjected to 1, 3 or 6 hours of moderate IRB (50% of the maximum inspiratory pressure) via a two way-non rebreathing valve. Quietly breathing animals served as controls. AMPK, Acetyl-CoA Carboxylase (ACC), CAMKK and STAT3 were evaluated by immunoblotting, GLUT4 expression and localization with immunohistochemistry, glycogen and glucose content spectrophotometrically. Results: IRB for 1h resulted in diaphragmatic glycogen depletion. Diaphragmatic glucose content increased at 6h of IRB, coinciding with an increase in both AMPK and ACC (its downstreat target) phosphorylation and in GLUT4 expression and translocation to the sarcolemma. CAMKK phosphorylation, a possible AMPK upstream regulator, was increased at 3h of IRB preceding AMPK activation. IRB for 6h resulted in glycogen depletion in the liver and increased STAT3 phosphorylation in both liver and diaphragm suggesting an active IL6-sugnalling. IRB-induced diaphragmatic IL6-upregulation was evidenced from the 1st hour of IRB. Conclusions: IRB leads to diaphragmatic and liver glycogen depletion, increased diaphragmatic GLUT4 expression and AMPK activation. Evidence exists for active IL6 signalling in the liver.