Effects of Muscle Length on Intracellular Ca2+ During Isometric Contraction of Tracheal Smooth Muscle
In both smooth and striated muscles, the active force a muscle can develop is related to its length. In striated muscles, the decrease in force that occurs as muscle length is decreased below the length of maximal active tension (LO) may result from a number of factors: length-dependent changes in the Ca2+-sensitivity of contractile proteins, length-dependent changes in the amount of activator Ca2+ supplied to contractile proteins, and mechanical factors affecting filament overlap (Gordon et al., 1966; Taylor and Rudel, 1970; Endo, 1973; Allen and Kurihara, 1982; Stephenson and Wendt, 1984; ). Studies of striated muscles, particularly cardiac muscle, suggest that as muscle length is decreased below LO there is a decrease in the activation of the myofilaments (Jewell,1977; Allen and Kurihara,1982; Stephenson and Wendt,1984). Also, when a striated muscle is allowed to shorten during active contraction, force redevelopment immediately after the shortening is reduced. This phenomenon, termed “shortening deactivation,” is dependent on Ca2+ and can be decreased or abolished by increasing the activation of the muscle ( Edman and Kiessling, 1971; Briden and Alpert, 1972; Bodem and Sonnenblick, 1974; Ekelund and Edman, 1982).
KeywordsIsometric Contraction Muscle Length Active Stress Calcium Transient Muscle Strip
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