Myosin light chain isoforms modify force-generating ability of cardiac myosin by changing the kinetics of actin-myosin interaction.
OBJECTIVE
To investigate the functional role of myosin light chain (MLC) isoforms in cardiac muscles, we examined the motor function of two different myosins the structure of which differed only in the MLC.


METHODS
We purified myosin from atria (A-myosin) and ventricles (V-myosin) of young rats, which contained atrial-type and ventricular-type MLCs, respectively, but having identical alpha-heavy chain isoform. Actin filament velocity (Vel) was determined in the in vitro motility assay. Average force of myosin molecules (F) was estimated and single events of actin-myosin interaction were recorded with the laser trap technique.


RESULTS
Vel was slightly higher in A-myosin than in V-myosin, while actin-activated ATPase activity was not different. F, determined from force versus actin filament length relation, was approximately 60% higher in V-myosin (3.3 vs. 2.1 pN/microm). The mean duration of isometric force events was longer in V-myosin than in A-myosin (323+/-13 vs. 294+/-30 ms, p<0.05), while the amplitudes of unitary displacement and force of a single myosin molecule did not differ between them.


CONCLUSIONS
The MLC isoform can be a determinant of force-generating ability of cardiac myosin by modulating crossbridge kinetics without affecting the catalytic activity.
Yamashita
Hiroshi
H
Department of Cardiovascular Medicine, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Tokyo 113-8655, Bunkyo, Japan. hiroyama-tky@umin.ac.jp
Sugiura
Seiryo
S
Fujita
Hideo
H
Yasuda
So ichiro
Si
Nagai
Ryozo
R
Saeki
Yasutake
Y
Sunagawa
Kenji
K
Sugi
Haruo
H
D008841:Actin Cytoskeleton / Q000502:physiology*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D018994:Myosin Light Chains / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D018994:Myosin Light Chains; D020033:Protein Isoforms; D000251:Adenosine Triphosphatases; D009218:Myosins