Sarcomere length-dependence of activity-dependent twitch potentiation in mouse skeletal muscle

✍ Scribed by Dilson E Rassier; Brian R MacIntosh

• Publisher: BioMed Central
• Year: 2002
• Tongue: English
• Weight: 551 KB
• Volume: 2
• Category: Article
• ISSN: 1472-6793
• DOI: 10.1186/1472-6793-2-19

✦ Synopsis

Background:

It has been reported that potentiation of a skeletal muscle twitch response is proportional to muscle length with a negative slope during staircase, and a positive slope during posttetanic potentiation. this study was done to directly compare staircase and posttetanic responses with measurement of sarcomere length to compare their length-dependence.

Methods:

Mouse extensor digitorum longus (edl) muscles were dissected to small bundles of fibers, which permit measurement of sarcomere length (sl), by laser diffraction. in vitro fixed-end contractions of edl fiber bundles were elicited at 22 degrees c and 35 degrees c at sarcomere lengths ranging from 2.35 microm to 3.85 microm. twitch contractions were assessed before and after 1.5 s of 75 hz stimulation at 22 degrees c or during 10 s of 10 hz stimulation at 22 degrees c or 35 degrees c.

Results:

Staircase potentiation was greater at 35 degrees c than 22 degrees c, and the relative magnitude of the twitch contraction (pt*/pt) was proportional to sarcomere length with a negative slope, over the range 2.3 microm - 3.7 microm. linear regression yielded the following: pt*/pt = -0.59 x sl+3.27 (r2 = 0.74); pt*/pt = -0.39 x sl+2.34 (r2 = 0.48); and pt*/pt = -0.50 x sl+2.45 (r2 = 0.80) for staircase at 35 degrees c, and 22 degrees c and posttetanic response respectively. posttetanic depression rather than potentiation was present at long sl. this indicates that there may be two processes operating in these muscles to modulate the force: one that enhances and a second that depresses the force. either or both of these processes may have a length-dependence of its mechanism.

Conclusion:

There is no evidence that posttetanic potentiation is fundamentally different from staircase in these muscles.