Submitted on November 1, 2004
Accepted on April 10, 2005
Effects of Endurance Exercise-Training on Single Fiber Contractile Properties of Insulin-treated Streptozotocin-Induced Diabetic Rats
Otto A. Sanchez1, LeAnn M. Snow2, Dawn A. Lowe3, Robert C. Serfass4, and LaDora V. Thompson5*
1 School of Kinesiology, University of Minnesota, Minneapolis, MN, USA; Department of Physiological Sciences, Universidad de Oriente, Ave Jose Mendez, Bolivar, Venezuela
2 School of Kinesiology, University of Minnesota, Minneapolis, MN, USA; Department of Physical Medicine and Rehabilitation, University of Minnesota Medical School, Minneapolis, MN, USA
3 Department of Physical Medicine and Rehabilitation, University of Minnesota Medical School, Minneapolis, MN, USA; Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota Medical School, Minneapolis, MN, USA
4 School of Kinesiology, University of Minnesota, Minneapolis, MN, USA
5 Department of Physical Medicine and Rehabilitation, University of Minnesota Medical School, Minneapolis, MN, USA
* To whom correspondence should be addressed. E-mail: thomp067{at}umn.edu.
Purpose: The purpose of this study was to characterize the contractile properties of individual skinned muscle fibers from insulin-treated streptozotocin (STZ)-induced diabetic rats after an endurance-exercise training program. We hypothesized that single fiber contractile function would decrease in the diabetic sedentary rats and that endurance exercise would preserve the function. Methods: Twenty-eight rats were assigned to either a non-diabetic sedentary, a non-diabetic exercise, a diabetic sedentary, or a diabetic exercise group. Rats in the diabetic groups received subcutaneous intermediate-lasting insulin daily. The exercise-trained rats ran on a treadmill at a moderate intensity for 60 min, 5 times per week. After 12 weeks, the extensor digitorum longus and soleus muscles were dissected. Single fiber diameter, Ca++-activated peak force, specific tension, activation threshold and pCa50 as well as the myosin heavy chain isoform expression (MHC) were determined. Results: In MHC type II fibers from EDL muscle, diameters were significantly smaller from diabetic sedentary rats in comparison to non-diabetic sedentary rats (p<0.001). Among the non-diabetic rats, fiber diameters were smaller with exercise (p=0.038). The absolute force generating capacity of single fibers was lower in muscles from diabetic rats. There was greater specific tension (force normalized to cross sectional area) by fibers from the rats that followed an endurance exercise program compared to sedentary. Conclusion: Alterations in the properties of contractile proteins are not implicated in the decrease in strength associated with diabetes and endurance-exercise training does not prevent or increase muscle weakness in diabetic rats.
