Myosin light chain-actin interaction regulates cardiac contractility.
The amino-terminal domain of the essential myosin light chain (MLC-1) binds to the carboxy terminus of the actin molecule. We studied the functional role of this interaction by two approaches: first, incubation of intact and chemically skinned human heart fibers with synthetic peptide corresponding to the sequences 5 through 14 (P5-14), 5 through 8 (P5-8), and 5 through 10 (P5-10) of the human ventricular MLC-1 (VLC-1) to saturate actin-binding sites, and second, incubation of skinned human heart fibers with a monoclonal antibody (MabVLC-1) raised against the actin-interacting N-terminal domain of human VLC-1 using P5-14 as antigen to deteriorate VLC-1 binding to actin. P5-14 increased isometric tension generation of skinned human heart fibers at both submaximal and maximal Ca2+ activation, the maximal effective peptide dosage being in the nanomolar range. A scrambled peptide of P5-14 with random sequence had no effects up to 10(-8) mol/L, ie, where P5-14 was maximally effective. P5-8 and P5-10 increased isometric force to the same extent as P5-14, but micromolar concentrations were required. Amplitude of isometric twitch contraction, rate of tension development, rate of relaxation, and shortening velocity at near-zero load of electrically driven intact human atrial fibers increased significantly on incubation with P5-14. These alterations were not associated with modulation of intracellular Ca2+ transients as monitored by fura 2 fluorescence measurements. Incubation of skinned human heart fibers with MabVLC-1 increased isometric tension at both submaximal and maximal Ca2+ activation levels, having a maximal effective concentration in the femtomolar range.
Morano
I
I
Max-Delbrück-Center for Molecular Medicine, Berlin, Germany.
Ritter
O
O
Bonz
A
A
Timek
T
T
Vahl
C F
CF
Michel
G
G
D000199:Actins / Q000378:metabolism*; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D006321:Heart / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D009218:Myosins / Q000737:chemistry / Q000378:metabolism*; D010455:Peptides / Q000138:chemical synthesis
D000199:Actins; D010455:Peptides; D009218:Myosins; D002118:Calcium