The role of thin filament cooperativity in cardiac length-dependent calcium activation.
Biophys J
; 99(9): 2978-86, 2010 Nov 03.
Article
em En
| MEDLINE
| ID: mdl-21044595
ABSTRACT
Length-dependent activation (LDA) is a prominent feature of cardiac muscle characterized by decreases in the Ca(2+) levels required to generate force (i.e., increases in Ca(2+) sensitivity) when muscle is stretched. Previous studies have concluded that LDA originates from the increased ability of (strong) cross-bridges to attach when muscle is lengthened, which in turn enhances Ca(2+) binding to the troponin C (TnC) subunit of the troponin complex. However, our results demonstrate that inhibition of strong cross-bridge attachment with blebbistatin had no effect on the length-dependent modulation of Ca(2+) sensitivity (i.e., EC(50)) or Ca(2+) cooperativity, suggesting that LDA originates upstream of cross-bridge attachment. To test whether LDA arises from length dependence of thin-filament activation, we replaced native cTnC with a mutant cTnC (DM-TnC) that is incapable of binding Ca(2+). Although progressive replacement of native cTnC with DM-TnC caused an expected monotonic decrease in the maximal force (F(max)), DM-TnC incorporation induced much larger increases in EC(50) and decreases in Ca(2+) cooperativity at short lengths than at long lengths. These findings support the conclusion that LDA arises primarily from the influence of length on the modulation of the Ca(2+) cooperativity arising from interaction between adjacent troponin-tropomyosin complexes on the thin filament.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Citoesqueleto de Actina
/
Sinalização do Cálcio
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Contração Miocárdica
Tipo de estudo:
Prognostic_studies
Limite:
Animals
/
Humans
/
Male
Idioma:
En
Ano de publicação:
2010
Tipo de documento:
Article