Takao Sugiura

Effects of heat stress and mechanical stretch on protein expression in cultured skeletal muscle cells

Effects of heat stress, mechanical stretching or a combination of both on the expression of heat shock proteins (HSPs) and total protein level were studied in a culture system. Rat skeletal muscle cells (L6) were cultured on flexible-bottomed culture plates. They were subjected to one of the four following conditions: (1) 97xa0h incubation at 37xa0°C, (2) 1xa0h incubation at 41xa0°C followed by 96xa0h incubation at 37xa0°C, (3) 1xa0h incubation at 37xa0°C followed by 96xa0h cyclic stretching (18% of initial length, 2-s stretch and 4-s release) at 37xa0°C or (4) 1xa0h incubation at 41xa0°C followed by 96xa0h cyclic stretching at 37xa0°C. The expression of HSP72 and HSP90 and total protein was determined in the crude homogenates, supernatant and pellets. Cellular protein concentrations in the homogenates and pellets were increased by heat stress and/or mechanical stress (stretch). A cumulative effect of the combination of heating and stretch on the protein concentration in the homogenates and in the pellets was noted. The expressions of HSP72 and HSP90 in the pellets were also increased by heat stress and/or stretch. However, HSP90 in the supernatant did not change following heat stress and/or stretch. The regulation of HSP72 and HSP90 expression in skeletal muscle cells may be closely related to total protein, the abundance of which is also stimulated by mechanical and heat stresses. These observations suggest strongly that heating and passive stretch of muscle may be useful as a means of increasing muscle mass, not only in athletes but also in patients during rehabilitation.