Characteristics of stretch-release induced tension development in arterial smooth muscle

Stretching helical strips of porcine a. carotis comm. to 1.7 times the resting length increases myosin light chain phosphorylation from 0.22 to 0.67 mol phosphate/mol light chain. While stretch is maintained, the stretch induced light chain phosphorylation decreases and reaches the resting level over a period of 60 minutes. The fully stretched arterial strips containing maximally phosphorylated myosin light chain cannot generate active tension which indicates, according to the sliding filament theory, the lack of overlap between actin and myosin filaments. When stretch is released from these muscle strips active tension develops. The amplitude of this stretch-release induced tension depends on the level of myosin light chain phosphorylation related to the time interval between stretch and release as well as on the extent of the overlap zone related to the length of the released strip. Three-dimensional graphic representation of both measured and interpolated data points in an active tension-light chain phosphorylation-muscle length space reveals a contractility surface which demonstrates that active tension appears as a sigmoidal function of light chain phosphorylation, on the one hand and shows maximum as a function of muscle length, on the other hand.