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This Article Full Text Full Text (PDF) All Versions of this Article: 584/2/591    most recent jphysiol.2007.138693v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by de Tombe, P. P. Articles by Stienen, G. J. M. Search for Related Content PubMed PubMed Citation Articles by de Tombe, P. P. Articles by Stienen, G. J. M. Related Collections Cardiovascular

¹ Center for Cardiovascular Research, Department of Physiology and Biophysics, University of Illinois at Chicago, IL 60612, USA
² Institute for Cardiovascular Research, Department of Physiology, Free University of Amsterdam, van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands

The dependence of contractile properties on intracellular calcium in cardiac tissue is a highly cooperative process. Here, the temperature and calcium dependence of contractile and energetical properties in permeabilized cardiac trabeculae from rat were studied to provide novel insights into the underlying kinetic processes. Myofilament Ca²⁺ sensitivity significantly increased with temperature between 15 and 25°C, whereas its steepness was independent of temperature. A direct proportionality between active tension and Ca²⁺-activated rate of ATP hydrolysis was observed; the slope of this relationship (tension cost) was highly temperature dependent. The rate of tension redevelopment following a quick release–restretch manoeuvre (k_tr) depended in a complex manner on the level of contractile activation and on temperature. At saturating calcium levels, the temperature dependence (Q₁₀) of k_tr and Ca²⁺-activated ATP hydrolysis rate were similar (Q₁₀ 3.5), and significantly higher than the Q₁₀ for maximum tension (T_max; Q₁₀ 1.3) or tension cost (Q₁₀ 2.5). In contrast, at a low level of contractile activation (5% of T_max), the Q₁₀ of k_tr was similar to that of tension cost, and significantly lower than the Q₁₀ of Ca²⁺-activated ATP hydrolysis at that level of contractile activation. Our results are consistent with the hypothesis that at high levels of contractile activation, the rates of tension redevelopment and Ca²⁺-activated ATP hydrolysis are determined by both apparent cross-bridge attachment and detachment rates, while at low levels, k_tr is limited by cross-bridge detachment rate. Tension cost, on the other hand, is determined solely by cross-bridge detachment kinetics at all temperatures and levels of contractile activation.

(Received 15 August 2007; accepted after revision 21 August 2007; first published online 23 August 2007)
Corresponding author P. P. de Tombe: Department of Physiology and Biophysics, MC 901, The University of Illinois at Chicago, 835 S. Wolcott Avenue, Chicago, IL 60607-7171, USA. Email: pdetombe{at}uic.edu

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