Kinetic properties of cardiac myosin heavy chain isoforms in rat.
The head portion of the myosin heavy chain (MHC) is essential in force generation. As previously shown, Ca2+-activated fibres of mammalian skeletal muscle display a strong correlation between their MHC isoform complement and the kinetics of stretch activation, suggesting isoform-specific differences in kinetic properties of myosin heads. Using the same methodology on muscle strips of atria and ventricles of hyper- and hypothyroid rats, this study showed that the kinetics of cardiac alphaMHC are 3 times faster than those of cardiac betaMHC under isometric conditions and maximal Ca2+ activation. Comparison of rat heart and skeletal muscle fibres revealed that 100% alphaMHC heart muscle strips exhibited faster stretch activation kinetics (time parameter t3: 108+/-18 ms, mean+/-SD) than rat type-IIA fibres ( t3: 157+/-19 ms), but slower than type-IID fibres ( t3: 55+/-10 ms). The kinetics of 100% betaMHC heart muscle strips ( t3: 351+/-44 ms) were faster than that of type-I fibres in rat skeletal muscle ( t3: 901+/-348 ms). This difference between the two muscle types calls in question the generally accepted identity of betaMHC and MHCIbeta.
Galler
Stefan
S
Zoologisches Institut, Universität Salzburg, Hellbrunnerstrasse 34, 5020 Salzburg, Austria. Stefan.Galler@sbg.ac.at
Puchert
Emma
E
Gohlsch
Bärbel
B
Schmid
Doris
D
Pette
Dirk
D
D000818:Animals; D006980:Hyperthyroidism / Q000503:physiopathology*; D007037:Hypothyroidism / Q000503:physiopathology*; D066298:In Vitro Techniques; D007537:Isometric Contraction; D007700:Kinetics; D008297:Male; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000503:physiopathology; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D020033:Protein Isoforms; D018995:Myosin Heavy Chains