Normalization of Mechanical Data

Maximal shortening velocities (V ,ax) nieasured in mammalian smooth muscle usually fall in the range 

7 Lq s i at 37°C, 50-100 times slower than that found in skeletal muscle. Several methods can be used to obtain generally there is a decrease in 

Other evidence suggests that the thick filaments in smooth muscle may be side-polar, that is, myosin molecules oriented in either direction are found along the whole length of the filament, with no central bare zone 

Progress has been made in defining molecular factors responsible for the variability in shortening velocity and ATPase rates between smooth muscles. Three types of isoform variations have been found in smooth muscle myosin (for reviews, see Somlyo, 1993, and Chapters 1 and 2 in this volume) (1) two variants in the tail region of the myosin heavy chain, one heavier (—204 kDa SM-1 and one lighter (—200 kDa SM-2)  

FIGURES Force responses (middle) to length ramps (upper) in a skinned guinea pig taenia coli fiber. Lower panel shows plots of force versus length during ramps. Stiffness increases with rate of length change. From Arheden and Hellstrand (1991). 

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