Effects of electrostimulation on glycogenolysis in cultured rat myotubes

Electrical pulse stimulation of cultured skeletal muscle cells as a model for in vitro exercise - possibilities and limitations

The beneficial health-related effects of exercise are well recognized, and numerous studies have investigated underlying mechanism using various in vivo and in vitro models. Although electrical pulse stimulation (EPS) for the induction of muscle contraction has been used for quite some time, its application on cultured skeletal muscle cells of animal or human origin as a model of in vitro exercise is a more recent development. In this review, we compare in vivo exercise and in vitro EPS with regard to effects on signalling, expression level and metabolism. We provide a comprehensive overview of different EPS protocols and their applications, discuss technical aspects of this model including critical controls and the importance of a proper maintenance procedure and finally discuss the limitations of the EPS model.

Intracellular generation of reactive oxygen species by contracting skeletal muscle cells

The aim of this work was to examine the intracellular generation of reactive oxygen species in skeletal muscle cells at rest and during and following a period of contractile activity. Intracellular generation of reactive oxygen species was examined directly in skeletal muscle myotubes using 2',7'-dichlorodihydrofluorescein (DCFH) as an intracellular probe. Preliminary experiments confirmed that DCFH located to the myotubes but was readily photoxidizable during repeated intracellular fluorescence measurements and strategies to minimize this were developed. The rate of oxidation of DCFH did not change significantly over 30 min in resting myotubes, but was increased by approximately 4-fold during 10 min of repetitive, electrically stimulated contractile activity. This increased rate was maintained over 10 min following the end of the contraction protocol. DCF fluorescence was distributed evenly throughout the myotube with no evidence of accumulation at any specific intracellular sites or localization to mitochondria. The rise in DCF fluorescence was effectively abolished by treatment of the myotubes with the intracellular superoxide scavenger, Tiron. Thus these data appear to represent the first direct demonstration of a rise in intracellular oxidant activity during contractile activity in skeletal muscle myotubes and indicate that superoxide, generated from intracellular sites, is the ultimate source of oxidant(s) responsible for the DCFH oxidation.