Passive and active mechanical properties of titin studied in intact frog muscle fibers upon inhibition of myosin motors by para-nitro-blebbistatin

In the striated muscle thousands of serially linked half-sarcomeres (the force generating units) make macroscopic the shortening but also imply instability, with lengthening of the weaker half-sarcomeres caused by shortening of the stronger ones. The giant protein titin spans the whole half-sarcomere, through the I-band, connecting the Z-line at the end of the sarcomere to the tip of the thick filament and through the A-band, associated to thick filament, up to M-line at the centre of the sarcomere.