HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 290/2/H886    most recent 00493.2005v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (4) Citing Articles via Google Scholar Google Scholar Articles by Gao, W. D. Articles by Nyhan, D. Search for Related Content PubMed PubMed Citation Articles by Gao, W. D. Articles by Nyhan, D.

Increased cross-bridge cycling rate in stunned myocardium

Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland

Submitted 13 May 2005 ; accepted in final form 13 September 2005

Decreased Ca²⁺ responsiveness of the myofilaments underlies myocardial stunning. Given that cross-bridge cycling is a major determinant of myofilament behavior, we quantified cross-bridge cycling rate in stunned myocardium. After stabilization, rat hearts were subjected to 20 min of no-flow global ischemia and 30 min of reperfusion at 37°C. Control hearts were perfused continuously at 37°C for 60 min. Trabeculae were dissected and chemically skinned with 1% Triton X-100. The muscles were then activated with solutions of varied Ca²⁺ concentration ([Ca²⁺]). Force-[Ca²⁺] relations, rate of force redevelopment after release (k_tr), muscle stiffness (k_m), and myofilament ATP consumption were determined. Maximal Ca²⁺-activated force (F_max) was depressed in stunned myocardium (49 ± 5 vs. 82 ± 5 mN/mm², P < 0.01). Western immunoblotting showed degradation of troponin I in stunned myocardium. The k_tr at F_max was significantly increased in stunned muscles (19.82 ± 2.74 vs. 13.19 ± 0.96 s^–1, 22°C, P < 0.01; 7.49 ± 0.52 vs. 5.81 ± 0.54 s^–1, 10°C, P < 0.05). The ratio of k_m measured at 100 Hz over that at 1 Hz, during F_max, is lower in stunned muscles (8.22 ± 1.56 vs. 12.94 ± 0.71, P < 0.05). In comparison with k_m at rigor, k_m at F_max is significantly lower in the stunned group (78.82 ± 6.11 vs. 93.27 ± 3.03%, P < 0.05). Myofilament ATP consumption at F_max did not change in stunned muscles (5,901 ± 952 vs. 5,596 ± 972 pmol·µl^–1·min^–1, P = 0.49). These results show that cross-bridge cycling is increased in stunned myocardium. Such increases are likely the result of increased transition rate from force-generating states to non-force-generating states. Thus stunned myocardium still maintains ATP consumption in spite of lower force development, rationalizing the long-standing paradox of decreased force but unchanged oxygen consumption in the postischemic heart.

cross-bridge cycling; contraction; myocardial stunning