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

Moreira CM, Meira EF, Vestena L, Stefanon I, Vassallo DV, Padilha AS - Clinics (Sao Paulo) (2012)

Bottom Line: 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.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.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.

View Article: PubMed Central - PubMed

Affiliation: Universidade Federal do Pampa, Uruguaiana, RS, Brasil.

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 shamoperated 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.

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Relationship between (A) the isometric force (g/mm2) or (B) the plateau tetanic tension and the myosin ATPase activity (nmol/Pi/min/mg) of the left ventricle in control, myocardial infarction, diabetic, DOCA-salt, L-NAME-treated, SHR, and WKY rats. The results represent the means ± SEM.
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f4-cln_67p489: Relationship between (A) the isometric force (g/mm2) or (B) the plateau tetanic tension and the myosin ATPase activity (nmol/Pi/min/mg) of the left ventricle in control, myocardial infarction, diabetic, DOCA-salt, L-NAME-treated, SHR, and WKY rats. The results represent the means ± SEM.

Mentions: Because our results were consistent with the previously reported controversies, we attempted to identify a correlation between mechanical changes and biochemical changes. According to Rundell et al. (17), the relationship between myosin ATPase activity and developed force provides information about the energetic cost of tension. As shown in Figure 4), in which force is plotted against myosin ATPase activity (tension cost) observed in the L-NAME, DOCA-salt, diabetic, Wistar control, SHR and WKY groups, there was a positive correlation among these variables under both normal conditions (Figure 4A) and with the use of tetanic plateau force (Figure 4B).


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

Moreira CM, Meira EF, Vestena L, Stefanon I, Vassallo DV, Padilha AS - Clinics (Sao Paulo) (2012)

Relationship between (A) the isometric force (g/mm2) or (B) the plateau tetanic tension and the myosin ATPase activity (nmol/Pi/min/mg) of the left ventricle in control, myocardial infarction, diabetic, DOCA-salt, L-NAME-treated, SHR, and WKY rats. The results represent the means ± SEM.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3351267&req=5

f4-cln_67p489: Relationship between (A) the isometric force (g/mm2) or (B) the plateau tetanic tension and the myosin ATPase activity (nmol/Pi/min/mg) of the left ventricle in control, myocardial infarction, diabetic, DOCA-salt, L-NAME-treated, SHR, and WKY rats. The results represent the means ± SEM.
Mentions: Because our results were consistent with the previously reported controversies, we attempted to identify a correlation between mechanical changes and biochemical changes. According to Rundell et al. (17), the relationship between myosin ATPase activity and developed force provides information about the energetic cost of tension. As shown in Figure 4), in which force is plotted against myosin ATPase activity (tension cost) observed in the L-NAME, DOCA-salt, diabetic, Wistar control, SHR and WKY groups, there was a positive correlation among these variables under both normal conditions (Figure 4A) and with the use of tetanic plateau force (Figure 4B).

Bottom Line: 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.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.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.

View Article: PubMed Central - PubMed

Affiliation: Universidade Federal do Pampa, Uruguaiana, RS, Brasil.

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 shamoperated 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.

Show MeSH
Related in: MedlinePlus