Evidence for cross bridge slippage in a stretched muscle fibre.

Bundles of glycerol-extracted psoas fibres which were contracted by immersion in a saline containing 15 mM MgATP and 12 micron free Ca++ were subjected to up to 3 stretches (rise time 0.8 msec) each of amplitude 1% Li at intervals of 10 msec. The elastic tension responses to these stretches were all of comparable size and the peak tensions reached during the stretches were in each case followed by a rapid tension decline almost to the tension values before the stretches. This indicates that stretch-induced detachment and reattachment of cross bridges to the actin filament occurred within 10 msec (slippage).