Hypothesis

            During muscle contractions cytosolic calcium and adenosine monophosphate activated protein kinase (AMPK) levels increase.  Exercise also increases GLUT 4 production, which allows more glucose to be metabolized in the muscle cell.  The purpose of this study was to determine whether calcium and AMPK cause the increases in GLUT 4 production in the cell.    

The hypothesis regarding GLUT 4 being tested in this research article stems from related research, which showed that GLUT 4 and mitochondria increase due to repeated bouts of muscle contraction.  Since raising calcium levels in the cytosol of the cell increases mitochondria, GLUT 4 is may increase as well.  The hypothesis that is being tested with this research was that GLUT 4 will be increased in skeletal muscle cells due to induced increases in the cytosolic calcium levels.  These calcium levels are increased in cells naturally due to exercise.  Since exercise also increases activity of AMPK, the study tested the effects of increasing AMPK on GLUT 4 levels in skeletal muscle.     

Methodology

            GLUT 4 levels were determined after exposing muscle cells to the various stimuli.  In order to test whether the various stimuli increased GLUT 4 muscle cells were either exposed to a single stimulus, a stimulus with an inhibitor specific of the stimulus, or no stimulus (control).  Then the GLUT 4 protein levels in each set of cells could be tested in order to determine the effects of each stimulus.  Various chemicals that are known to be produced in a muscle cell during normal exercise were used as stimuli.  Caffeine, which produces increased cytosolic calcium, was used to simulate the normal increase in calcium in a cell during exercise.  Another chemical produced during exercise and believed to be involved in GLUT 4 transport is AMPK, which can be induced pharmacologically through the addition of AICAR, was also used.