The Latch State in Skinned Fibers

In intact smooth muscle, phosphorylation often declines while force is maintained, the so-called latch state (Dillon etal., 1981). Regulation of the latch state is still poorly understood. It has been very difficult to induce a latch state in skinned smooth muscle. The closest may be triton skinned chicken gizzard, which contracts independent of MLC phosphorylation (Wagner and Ruegg, 1986). In skinned chicken gizzard, but also in other types of smooth muscle (Bialojan et al., 1987 Siegman et al., 1989 Kenney et al., 1990 Schmidt et al, 1995), a steep and nonlinear relation between force and MLC phosphorylation was observed, which was postulated by the latch model of Hai and Mur- 

KINETIC INVESTIGATIONS IN PERMEABILIZED SMOOTH MUSCLE USING CAGED COMPOUNDS 

By using caged compounds in combination with permeabilized smooth muscle preparations, valuable information regarding the rate-limiting steps between excitation and contraction (see Somlyo and Somlyo, 1990, for review Somlyo et al., 1992), regulation of Ca + release from the SR (Walker et al., 1987 lino and Endo, 1992), and the kinetics of the cross-bridge cycle (Arner et al., 1987 Somlyo et al, 1988 Fuglsang et al, 

1993) was obtained. Differences between tonic and phasic smooth muscle could be ascribed to the different kinetics of the phosphorylation reaction and crossbridge cycle (Fuglsang et al., 1993). 

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