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- Olsson, M Charlotte, et al.
(författare)
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Basal myosin light chain phosphorylation is a determinant of Ca2+ sensitivity of force and activation dependence of the kinetics of myocardial force development
- 2004
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Ingår i: American Journal of Physiology. Heart and Circulatory Physiology. - Bethesda : American Physiological Society. - 0363-6135 .- 1522-1539. ; 287:6, s. H2712-H2718
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Tidskriftsartikel (refereegranskat)abstract
- It is generally recognized that ventricular myosin regulatory light chains (RLC) are ∼40% phosphorylated under basal conditions, and there is little change in RLC phosphorylation with agonist stimulation of myocardium or altered stimulation frequency. To establish the functional consequences of basal RLC phosphorylation in the heart, we measured mechanical properties of rat skinned trabeculae in which ∼7% or ∼58% of total RLC was phosphorylated. The protocol for achieving ∼7% phosphorylation of RLC involved isolating trabeculae in the presence of 2,3-butanedione monoxime (BDM) to dephosphorylate RLC from its baseline level. Subsequent phosphorylation to ∼58% of total was achieved by incubating BDM-treated trabeculae in solution containing smooth muscle myosin light chain kinase, calmodulin, and Ca2+ (i.e., MLCK treatment). After MLCK treatment, Ca2+ sensitivity of force increased by 0.06 pCa units and maximum force increased by 5%. The rate constant of force development ( ktr) increased as a function of Ca2+ concentration in the range between pCa 5.8 and pCa 4.5. When expressed versus pCa, the activation dependence of ktr appeared to be unaffected by MLCK treatment; however, when activation was expressed in terms of isometric force-generating capability (as a fraction of maximum), MLCK treatment slowed ktr at submaximal activations. These results suggest that basal phosphorylation of RLC plays a role in setting the kinetics of force development and Ca2+ sensitivity of force in cardiac muscle. Our results also argue that changes in RLC phosphorylation in the range examined here influence actin-myosin interaction kinetics differently in heart muscle than was previously reported for skeletal muscle.
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| 2. |
- Stelzer, J E, et al.
(författare)
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Expression of cardiac troponin T with COOH-terminal truncation accelerates cross-bridge interaction kinetics in mouse myocardium
- 2004
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Ingår i: American Journal of Physiology. Heart and Circulatory Physiology. - Bethesda : American Physiological Society. - 0363-6135 .- 1522-1539. ; 287:4, s. H1756-H1761
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Tidskriftsartikel (refereegranskat)abstract
- Transgenic mice expressing an allele of cardiac troponin T (cTnT) with a COOH-terminal truncation (cTnTtrunc) exhibit severe diastolic and mild systolic dysfunction. We tested the hypothesis that contractile dysfunction in myocardium expressing low levels of cTnTtrunc (i.e., <5%) is due to slowed cross-bridge kinetics and reduced thin filament activation as a consequence of reduced cross-bridge binding. We measured the Ca2+ sensitivity of force development [pCa for half-maximal tension generation (pCa50)] and the rate constant of force redevelopment ( ktr) in cTnTtrunc and wild-type (WT) skinned myocardium both in the absence and in the presence of a strong-binding, non-force-generating derivative of myosin subfragment-1 (NEM-S1). Compared with WT mice, cTnTtrunc mice exhibited greater pCa50, reduced steepness of the force-pCa relationship [Hill coefficient ( nH)], and faster ktr at submaximal Ca2+ concentration ([Ca2+]), i.e., reduced activation dependence of ktr. Treatment with NEM-S1 elicited similar increases in pCa50 and similar reductions in nH in WT and cTnTtrunc myocardium but elicited greater increases in ktr at submaximal activation in cTnTtrunc myocardium. Contrary to our initial hypothesis, cTnTtrunc appears to enhance thin filament activation in myocardium, which is manifested as significant increases in Ca2+-activated force and the rate of cross-bridge attachment at submaximal [Ca2+]. Although these mechanisms would not be expected to depress systolic function per se in cTnTtrunc hearts, they would account for slowed rates of myocardial relaxation during early diastole.
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