Tension cost correlates with mechanical and biochemical parameters in different myocardial contractility conditions

Abstract

OBJECTIVES:Tension cost, the ratio of myosin ATPase activity to tension, reflects the economy of tension development in the myocardium. To evaluate the mechanical advantage represented by the tension cost, we studied papillary muscle contractility and the activity of myosin ATPase in the left ventricles in normal and pathophysiological conditions.METHODS:Experimental protocols were performed using rat left ventricles from: (1) streptozotocin-induced diabetic and control Wistar rats; (2) N-nitro-L-arginine methyl ester (L-NAME) hypertensive and untreated Wistar rats; (3) deoxycorticosterone acetate (DOCA) salt-treated, nephrectomized and salt- and DOCA-treated rats; (4) spontaneous hypertensive rats (SHR) and Wistar Kyoto (WKY) rats; (5) rats with myocardial infarction and sham-operated rats. The isometric force, tetanic tension, and the activity of myosin ATPase were measured.RESULTS:The results obtained from infarcted, diabetic, and deoxycorticosterone acetate-salt-treated rats showed reductions in twitch and tetanic tension compared to the control and sham-operated groups. Twitch and tetanic tension increased in the N-nitro-L-arginine methyl ester-treated rats compared with the Wistar rats. Myosin ATPase activity was depressed in the infarcted, diabetic, and deoxycorticosterone acetate salt-treated rats compared with control and sham-operated rats and was increased in N-nitro-L-arginine methyl ester-treated rats. These parameters did not differ between SHR and WKY rats. In the studied conditions (e.g., post-myocardial infarction, deoxycorticosterone acetate salt-induced hypertension, chronic N-nitro-L-arginine methyl ester treatment, and streptozotocin-induced diabetes), a positive correlation between force or plateau tetanic tension and myosin ATPase activity was observed.CONCLUSION:Our results suggest that the myocardium adapts to force generation by increasing or reducing the tension cost to maintain myocardial contractility with a better mechanical advantage.

Energy expenditure for isometric contractions of right and left ventricular trabeculae over a wide range of frequencies at body temperature

“…Slowed kinetics has been ascertained from a reduction of maximal dS/dt 22,23 , paralleled by a shift in the myosin heavy chain isoform (MHC) from predominantly α (fast) to predominantly β (slow) 23,30–35 . These observations have led to the notion that slowing of contractile kinetics is an adaptive response that increases the economy of contraction 22,23,31,33,34,37,38 .…”

Adipose Mesenchymal Cells-Derived EVs Alleviate DOCA-Salt-Induced Hypertension by Promoting Cardio-Renal Protection

“…Animal studies were run in accordance with the Brazilian College of Animal guidelines, with all procedures receiving approval from the Institutional Committee for Animal Care and Use of the Federal University of Rio de Janeiro (CEUA, certificate 038/15 and A02/16-61-15). The DOCA-salt model was generated by a modified protocol from 59 . 7-week-old male Wistar rats were obtained from the animal facility of Biomedical Science Institute, University of São Paulo (São Paulo, Brazil).…”

“…The DOCA-salt model was generated by a modified protocol from. 59 7-week-old male Wistar rats were obtained from the animal facility of Biomedical Science Institute, University of São Paulo (São Paulo, Brazil). After 1 week of acclimatization, animals were anesthetized by intraperitoneal injection of xylazine (5 mg/kg; Bayer S.A., São Paulo, Brazil) and ketamine (50 mg/kg; Cristália, Itapira, Brazil) and underwent unilateral nephrectomy (left kidney).…”