Original article Acto-myosin crossbridge kinetics in humans with coronary artery disease: Influence of sex and diabetes mellitus Naomi K. Fukagawa a, *, Bradley M. Palmer b , William D. Barnes b , Bruce J. Leavitt c , Frank P. Ittleman c , Martin M. LeWinter a , David W. Maughan b a Department of Medicine, University of Vermont College of Medicine, 89 Beaumont Avenue, Given C-207, Burlington, VT 05405-0068, USA b Department of Molecular Physiology and Biophysics, University of Vermont College of Medicine, 89 Beaumont Avenue, Burlington, VT 05405, USA c Department of Surgery, University of Vermont College of Medicine, 89 Beaumont Avenue, Burlington, VT 05405, USA Received 10 December 2004; revised and accepted 13 June 2005 Available online 19 September 2005 Abstract Risk of heart failure (HF) is influenced by sex and diabetes mellitus (DM). To better understand these interactions, sub-epicardial myocar- dium from 26 patients with coronary artery disease (CAD) undergoing coronary bypass surgery was examined in vitro using sinusoidal length perturbation analysis at varying [Ca 2+ ] to determine the viscoelastic properties of myofilaments related to acto-myosin crossbridge kinetics. Half of the patients had CAD only (four female, F-CAD; nine male, M-CAD), while the other half had both CAD and Type 2 DM (six F-DM; seven M-DM). At maximal and sub-maximal myofilament Ca 2+ activation there was a significant effect of sex and disease on frequency of maximum oscillatory work output during sinusoidal perturbation (P < 0.05). Myofilaments from F-CAD produced oscillatory work at sig- nificantly higher frequencies compared with M-CAD, while myofilaments from F-DM and M-DM produced work at similar frequencies. Correspondingly, minimum viscoelastic stiffness at maximum Ca 2+ activation occurred at significantly higher frequencies in F-CAD (5.0 ± 0.3 Hz) than M-CAD (3.3 ± 0.3 Hz), but at similar frequencies in F-DM (3.7 ± 0.3 Hz) and M-DM (4.3 ± 0.2 Hz). Thus, sex influences acto-myosin crossbridge kinetics in myofilaments isolated from CAD patients. These sex-related differences were absent in DM, suggesting that differences in the properties of cardiac muscle contribute to reported sex differences in the incidence and mortality of HF in DM. © 2005 Elsevier Ltd. All rights reserved. Keywords: Sex; Diabetes mellitus; Heart failure; Oscillatory work; Coronary artery disease; Myofilaments; Acto-myosin crossbridge kinetics 1. Introduction Type 2 diabetes mellitus (DM) is a major risk factor for heart failure (HF) [1–3] and a number of observations indi- cate that a subclinical cardiomyopathy exists in many DM patients. Thus, DM patients without overt evidence of car- diac disease have a high incidence of mitral inflow velocity abnormalities consistent with diastolic dysfunction [4–6], increased ultrasonic backscatter suggestive of structural alter- ations in myocardial connective tissue [7] and abnormal ven- tricular functional responses during stress [8,9]. Moreover, DM patients suffering a first myocardial infarction (MI) have a markedly increased risk of developing HF, independent of MI size [10,11]. Women with DM are at considerably higher risk than men for development of HF [3,12] including the post-MI period [13,14], suggesting that some component(s) of DM-related cardiomyopathy is determined by sex. In gen- eral, sex is a potent modifier of cardiovascular pathophysiol- ogy, including coronary artery disease (CAD) [6]. Although statistics linking mortality to cardiovascular dis- ease indicate that sex-related differences tend to be attenu- ated with advancing age, such differences are not simply due to the presence of estrogen. A recent report shows that estro- gen replacement in postmenopausal women actually increases the morbidity and mortality from heart disease [12]. Thus, the basis for sex-related differences in the development and outcome of cardiovascular disease, including the modulatory effects of DM, remains elusive. Alterations in myocardial properties related to cross- bridge kinetics have an important impact on effects of con- traction frequency and contractile reserve [15,16]. This is * Corresponding author. Tel.: +1 802 656 4403; fax: +1 802 656 2636. E-mail address: Naomi.Fukagawa@uvm.edu (N.K. Fukagawa). Journal of Molecular and Cellular Cardiology 39 (2005) 743–753 www.elsevier.com/locate/yjmcc 0022-2828/$ - see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.yjmcc.2005.06.010