Force generated by non-cycling crossbridges at low ionic strength in skinned smooth muscle from Taenia coli

In skinned smooth muscle preparations of Taenia coli from guinea pig the cyclic actin-myosin-interaction is inhibited to resting levels whereas the force remains high when in the contracted muscle the ionic strength of the incubation solutions is lowered from 65 mM to 18 mM. In accordance with a strongly depressed ATPase activity under these conditions the isotonic shortening velocity is drastically decreased suggesting that crossbridges are not cycling (latch-state). Since the Ca2+ concentration is kept constant (4 X 10(-5) M) and the phosphorylation of the myosin light chain (LC) is found to be unchanged it must be concluded that the formation of latch-bridges is not necessarily dependent on a change in the Ca2+ concentration or the state of phosphorylation.