Human myocardial responses depend on preparation and activation conditions. Nonfailing permeabilized single cardiomyocytes exposed to 1 µM omecamtiv mecarbil showed increased force at submaximal calcium but reduced maximal calcium-activated force, together with slower activation and relaxation and increased passive force. In failing multicellular myocardial preparations, 1 and 10 µM increased calcium sensitivity and slowed tension redevelopment without significantly changing maximal force. The reason for the different maximal-force responses remains undetermined. [2,1]
Actin-activated ATPase of human β-cardiac myosin S1
Biochemical assay · Purified recombinant human β-cardiac myosin subfragment 1 (M2β-S1); associated mouse light chains characterized in the original paper. [1]
OM reduced maximal actin-activated ATPase turnover and the actin concentration for half-maximal activity. The OM concentration-response endpoint was ATPase inhibition, despite the cardiac-myosin-activator designation.
Literature-Reported Treatment Conditions
- Treatment concentration
- 10 µM OM for actin-dependence comparison; varying OM for concentration-response at 40 µM actin
- Exposure duration
- NADH absorbance monitored for 200 s
- Method
- NADH-linked ATPase assay; 100 nM M2β-S1, 0–60 µM actin, 1 mM MgATP in MOPS20 buffer (20 mM KCl)
- Vehicle
- 0.1% DMSO comparison; buffer-only control also tested
- Reported limits
- ATPase assay temperature is not specified in the acquired Steady-state ATPase Activity subsection.
Methods and source locations
Compound reported in the paper: Omecamtiv mecarbil; Compound label in the paper: OM (CK-1827452)
Evidence concerns the named research compound in the reported preparation; no salt conversion or validation of the current Adooq lot.
Results: Actin-activated ATPase of M2β-S1; Fig. 2A-B; Table 1; Experimental Procedures: Reagents and Buffers, Steady-state ATPase Activity
Maximum actin-activated ATPase turnover: Hyperbolic fit versus actin concentration. Fig. 2 caption describes error bars as standard deviation of the mean from three protein preparations. — Table 1: 20 mM KCl + DMSO and 20 mM KCl + OM; Fig. 2A caption
Actin concentration for half-maximal ATPase activity: Michaelis-Menten actin-dependence fit; this is actin concentration, not OM potency. — Table 1: 20 mM KCl + DMSO and 20 mM KCl + OM
Concentration-dependent inhibition of actin-activated ATPase: OM concentration-response at 40 µM actin; fit to Equation 1. The result sentence does not separately define the ± term for this fitted EC50. — Results: Actin-activated ATPase of M2β-S1; Fig. 2B
Mechanics of permeabilized failing human myocardium
Cell-based study · 46 chemically permeabilized multicellular preparations from subendocardial left ventricular tissue of eight patients with end-stage heart failure; 15 °C, sarcomere length 2.24 µm. [1]
OM at 1 and 10 µM increased calcium sensitivity and slowed tension redevelopment. Maximum isometric force at pCa 4.5 was not significantly changed.
Literature-Reported Treatment Conditions
- Treatment concentration
- 0 (control), 0.1, 1.0 or 10 µM OM; one concentration per preparation
- Exposure duration
- At least 3 min in relaxing solution containing the assigned OM concentration between trials
- Method
- Force-pCa curves and rapid shortening/re-stretch tension-recovery measurements; ionic strength 180 mM
- Vehicle
- 0.67% DMSO in every experimental solution
- Reported limits
- No exact values inferred from the Fig. 8 bars.
Methods and source locations
Compound reported in the paper: Omecamtiv mecarbil; Compound label in the paper: OM (CK-1827452)
Evidence concerns the named research compound in the reported preparation; no salt conversion or validation of the current Adooq lot.
Results: Muscle Mechanics of Human Myocardium; Fig. 8; Experimental Procedures: Human Tissue through Statistics for Muscle Mechanics
Maximal isometric force at pCa 4.5: 46 preparations from eight hearts across all conditions; linear mixed model, Tukey-Kramer post hoc correction; total is not per-group n. — Results: Muscle Mechanics of Human Myocardium; Fig. 8A
Calcium sensitivity of force: Force-pCa relationship; image checked for direction, no bar-derived decimals. — Results: Muscle Mechanics of Human Myocardium; Fig. 8C image (caption panel labels reversed)
Rate of tension redevelopment: Rapid shortening/re-stretch and single-exponential recovery fit; image checked for direction. — Results: Muscle Mechanics of Human Myocardium; Fig. 8B image (caption panel labels reversed)
Force and calcium sensitivity in nonfailing human cardiomyocytes
Cell-based study · Permeabilized nonfailing human left ventricular cardiomyocytes at 15 °C and sarcomere length 2.3 µm. Supplement specifies four hearts for force measurements, 5–6 cells per heart; Fig. 1 specifies seven to nine determinations. [2]
OM increased calcium sensitivity and force at submaximal calcium, but reduced maximal calcium-activated force at 1 µM. Activation and relaxation slowed and passive force increased.
Literature-Reported Treatment Conditions
- Treatment concentration
- 0.1 and 1 µM OM for force-pCa curves; concentration-response measurements also shown in Fig. 1
- Exposure duration
- Incubation duration is not specified in the acquired human-cell force methods
- Method
- Isometric single-cell mechanics; comparisons with baseline without OM
- Vehicle
- DMSO stock solvent; final bath fraction not specified in the acquired force methods
- Reported limits
- Main Methods describes five donor hearts overall; supplement specifies four for force measurements. Exact per-condition allocation and incubation duration are not supplied in these passages.
Methods and source locations
Compound reported in the paper: Omecamtiv mecarbil; Compound label in the paper: OM
Evidence concerns the named research compound in the reported preparation; no salt conversion or validation of the current Adooq lot.
Methods: Human tissue source, Mechanical measurements, OM; Results first subsection; Fig. 1; Supplementary file2: Mechanical measurements on permeabilized myocytes, Statistics
Calcium sensitivity of isometric force: Mean ± SEM; Fig. 1 reports seven to nine individual measurements. — Results first subsection; Fig. 1C-D
Active force at submaximal calcium, pCa 6.2: Isometric force normalized to cell cross-sectional area; mean ± SEM. — Results first subsection; Fig. 1E
Active force at maximal activation, pCa 4.75: Isometric force normalized to cell cross-sectional area; mean ± SEM. — Results first subsection; Fig. 1E
