Depressed cardiac tension cost in experimental diabetes is due to altered myosin heavy chain isoform expression

Abstract

Rundell, Veronica L. M., David L. Geenen, Peter M. Buttrick, and Pieter P. de Tombe. Depressed cardiac tension cost in experimental diabetes is due to altered myosin heavy chain isoform expression. Am J Physiol Heart Circ Physiol 287: H408 -H413, 2004. First published March 4, 2004 10.1152/ajpheart.00049.2004.-Cardiac disease in diabetes presents as impaired left ventricular contraction and relaxation; however, the mechanisms underlying contractile protein dysfunction during the progression of disease are unknown. Accordingly, we assessed Ca 2ϩ -dependent tension development and tension-dependent ATP consumption (tension cost) in a rat model early (6 wk) and late (12 wk) after the onset of diabetes (50 mg/kg iv streptozotocin) using mechanical force-and enzyme-coupled UV absorbance measurements. Myofilament Ca 2ϩ sensitivity and maximal tension were unchanged between groups at either time point. Cross-bridge cycling rate was significantly decreased in diabetes, as indexed by tension cost (early control 5.4 Ϯ 0.4 and early diabetes 4.2 Ϯ 0.3; and late control 6.0 Ϯ 0.2 and late diabetes 4.2 Ϯ 0.2; P Ͻ 0.05). Because rodent models of cardiac disease are confounded by altered myosin isoform distribution, myosin content was determined by SDS-PAGE and densitometry. The cardiac content of ␣-myosin in diabetes was decreased to 41% Ϯ 4.1 at 6 wk and 32.5% Ϯ 2.9 at 12 wk of diabetes (early control 77.8% Ϯ 3.3 and late control 73.6% Ϯ 2.5). Separate control experiments demonstrated a linear decrease in tension cost with decreased ␣-myosin content. Given this, the depression of tension cost in this rodent model of diabetes could be fully explained by the altered myosin isoform distribution.cross-bridge cycling; cardiac energetics DIABETES MELLITUS is associated with a cardiomyopathy (CM), which develops in the absence of underlying coronary vascular disease in humans and rodents (12,26). This CM is associated with impaired left ventricular contraction and relaxation (4,22). Because diabetes affects Ͼ15 million Americans and approximately ϳ75% of these individuals will die of cardiovascular disease, it is important to ascertain what specific contractile deficits are present in diabetic CM.Accordingly, models of experimental diabetes have been generated to explore the molecular alterations that occur in diabetic CM. In brief, excitation-contraction coupling and the kinetics of shortening and relaxation are generally depressed in these preparations, regardless of peak shortening defects (17,23,24). In terms of the energetics of contraction, cross-bridge cycling and Ca 2ϩ sensitivity of Ca 2ϩ -dependent actin-activated MgATPase have been reported to be altered in diabetes (17,18). Alterations in maximal tension development have not been described; however, controversy exists with regard to Ca 2ϩ sensitivity of myofilaments in multicellular preparations (1, 17). Likewise, in isolated single cell preparations there have been reports of normal (17, 24), increased (28), and decreased peak shortening (23). Thus diabetic myocardium...

Development of contractile dysfunction in rat heart failure: hierarchy of cellular events

“…2). We have recently demonstrated that increased ␤-MHC content in rat myocardium correlates with reduced tension cost (35,36). Therefore, the depression of F max and tension cost seen in the late HF group could be due merely to altered isomyosin composition.…”

“…A new finding in the present study is the reduction in cross-bridge cycling rate that accompanied the depression of myofilament force development at end-stage HF. It is well established that ␤-myosin is associated with a reduction in cross-bridge cycling (35,36). Therefore, reduced cross-bridge cycling may merely have been the result of altered isomyosin composition in HF.…”

“…Skinned trabeculae were prepared by exposure to relaxing solution with 1% Triton X-100 at 4°C for at least 2 h (7,9). Skinned trabeculae were then attached to aluminum T-clips and mounted in an experimental setup that allows for simultaneous measurement of calcium-activated myofilament force and ATP hydrolysis rate (9,35,36). Finally, following dissection of suitable trabeculae, the left ventricle (LV) was cut transversely at the base of the papillary muscles to measure its unstressed diameter.…”

“…Next, twitch force was measured over a range of [Ca 2ϩ ]o at SL ϭ 2.0 m to evaluate the twitch force- [Ca 2ϩ ]o relationship (7,10). Skinned trabeculae were bathed in a series of solutions with varied activating calcium levels to compile the steady state contractile force-free [Ca 2ϩ ] and forceATPase relationships (9,35,36).…”

Celecoxib and 2,5-Dimethyl-Celecoxib Prevent Cardiac Remodeling Inhibiting Akt-Mediated Signal Transduction in an Inherited Dilated Cardiomyopathy Mouse Model

“…Myosin heavy chain (MyHC) isoforms in the LV myocardium were separated on SDS-polyacrylamide gel electrophoresis according to the method of Rundell et al (2004). We applied an equal amount of protein in each lane (10 g/lane).…”