Journal
PFLUGERS ARCHIV-EUROPEAN JOURNAL OF PHYSIOLOGY
Volume 449, Issue 5, Pages 449-457Publisher
SPRINGER HEIDELBERG
DOI: 10.1007/s00424-004-1354-6
Keywords
calcium sensitivity; myocardium; sarcomere length; X-ray diffraction
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Funding
- NCRR NIH HHS [RR08630] Funding Source: Medline
- NHLBI NIH HHS [HL62881] Funding Source: Medline
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The effect of titin-based passive tension on Ca2+ sensitivity of active tension and interfilament lattice spacing was studied in skinned rat ventricular trabeculae by measuring the sarcomere length (SL)dependent change in Ca2+ sensitivity and performing small angle X-ray diffraction studies. To vary passive tension, preparations were treated with trypsin at a low concentration (0.31 mug/ml) for a short period (13 min) at 20degreesC, that resulted in similar to40% degradation of the I-band region of titin, with a minimal effect on A-band titin. We found that the effect of trypsin on titin-based passive tension was significantly more pronounced immediately after stretch than at steady state, 30 min after stretch (i.e., trypsin has a greater effect on viscosity than on elasticity of passive cardiac muscle). Ca2+ sensitivity was decreased by trypsin treatment at SL 2.25 mum, but not at SL 1.9 mum, resulting in marked attenuation of the SL-dependent increase in Ca2+ sensitivity. The SL-dependent change in Ca2+ sensitivity was significantly correlated with titin-based passive tension. Small-angle X-ray diffraction experiments revealed that the lattice spacing expands after trypsin treatment, especially at SL 2.25 mum, providing an inverse linear relationship between the lattice spacing and Ca2+ sensitivity. These results support the view that titin-based passive tension promotes actomyosin interaction and that the mechanism includes interfilament lattice spacing modulation.
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