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A study showed that inhibition of myo-inositol-1-monophosphatase (IMPase) and elevation of inositol monophosphatases do not mediate the stimulatory effect of lithium on glucose transport in fat cells of rats. The finding is based on the comparison of the effects of lithium and a selective inhibitor (IMPase), L-690,488 on glucose transport. The effects were determined using the nonparametric ANOVA and the least squares means method for paired groups.

An experiment was conducted to reinvestigate the role of epinephrine and other beta-adrenergic catecholamines on insulin-dependent glucose transport of skeletal muscle. Results indicated that although epinephrine inhibited the uptake of glucose, the glucose transport process was not affected. The inhibitory effect of epinephrine was attributed to its ability to stimulate glycogenolysis that resulted in the inhibition of muscle hexokinase by increasing the levels of glucose-6-phosphate.

The activity of the hexosamine synthesis pathway was analyzed in ob/ob mice models of insulin resistance to determine its role in the development of resistance to the biological activity of insulin. Analysis of insulin responsiveness to glucose transport in the isolated soleus muscles of ob/ob mice indicated the presence of marked insulin resistance. Furthermore, the muscles of ob/ob mice exhibited decreased insulin binding due to defective insulin receptor-response coupling.

The addition of Ca2+ ionophore ionomycin to fat cells and skeletal muscles inhibits the insulin-activated glucose transport while it has no effect on the basal glucose transport. On the other hand, in frog sartorius muscle, an increase in the cytoplasmic Ca2+ increases the K+-stimulated glucose transport. The inhibition of the insulin-stimulated glucose transport is not a result of an increase in the adenosine 3',5'-cyclic monophosphate but actually of the Ca2+. The results of this study show that a sustained influx of Ca2+ inhibits the glucose transport activity stimulated by Ca2+ but stimulates the glucose activity in muscle.

Analysis of the influence of muscle contractions and insulin on glucose transport kinetics in isolated rat skeletal muscles shows that insulin and muscle contractions enhance the maximal transport velocity in an additive manner and thus promote glucose transport. The apparent half-maximal saturating substrate concentration for the insulin-stimulated and basal glucose transport are similar in the muscles.

Glucose transport is stimulated by the contractions/hypoxia pathway by W-7, which produces Ca2+ from sarcoplasmic reticulum. This indicates that cytosolic Ca2+ increment stimulates contractile activity in manner similar to hypoxia initiating glucose transport in striated muscles. W-7 also inhibits glucose transport stimulation by insulin.

Rat-epitrochlearis muscles incubated in vitro contracted 15 minutes after incubation, and when stimulated, caused an enhanced insulin sensitivity. No similar effects resulted when washed muscles were stimulated to contract in vitro. Enhanced proneness of glucose transport to insulin simulation results from the action of a proteinaceous serum and contractiles.

The GLUT-4 glucose transporter concentration and the glucose transport activity in skeletal muscles of female Long-Evans rats are influenced by growth and aging. The presumption that skeletal muscle shows the formation of insulin resistance due to aging is analyzed. Immunoblotting with a polyclonal antibody directed against GLUT-4 is used to calculate the varying quantities of immunoreactive GLUT-4 protein in muscle homogenates of 1-, 10-, and 25-month-old rats. A fall in GLUT-4 immunoreactivity is seen in the epitrochlearis, plantaris and the red and white areas of the quadriceps muscles. Identical GLUT-4 concentration is observed in flexor digitorum brevis and soleus muscles.