Effects of BDM, [Ca²⁺]_o, and temperature on the dynamic stiffness of quiescent cardiac trabeculae from rat

Abstract

([Ca 2ϩ ]o). More recently, the negative inotropic agent 2,3-butanedione monoxime (BDM) has been used. However, there remains a lack of data regarding the influence of temperature, Ca 2ϩ , and BDM on the passive mechanical properties of cardiac tissue. We have used the dynamic stiffness technique, a sensitive measurement of cross-bridge activity, in which minute (ϳ0.2% of muscle length) sinusoidal perturbations are applied at various frequencies (0.2-100 Hz) to quiescent, viable right ventricular rat trabeculae at two temperatures (20°C and 26°C) and at two [Ca 2ϩ ]o (0.5 and 1.25 mM) in the presence and absence of BDM (20 mM). The stiffness spectra (amplitude and phase) were sensitive to temperature and [Ca 2ϩ ]o in the absence of BDM but insensitive in the presence of BDM. From the index of cross-bridge cycling (the ratio of high-to low-frequency stiffness amplitude), we infer that BDM inhibits a small degree of spontaneous sarcomere activity, thereby allowing the true passive properties of trabeculae to be determined. In the absence of BDM, the extent of spontaneous sarcomere activity decreases with increasing temperature. We caution that the measured mechanical properties of passive cardiac tissue are critically dependent on the experimental conditions under which they are measured. Experiments must be performed at sufficiently high temperatures (Ͼ25°C) to ensure a low resting concentration of intracellular Ca 2ϩ or in the presence of an inhibitor of cross-bridge cycling. cardiac muscle; sinusoidal length perturbation; passive mechanics; 2,3-butanedione monoxime; extracellular calcium concentration THE MECHANICAL PROPERTIES of passive cardiac tissue are important, inasmuch as they help determine the stroke volume of the heart (3) and, hence, play a major role in diastolic dysfunction observed clinically. Mechanical tests are commonly performed on isolated hearts or samples of cardiac tissue and are conducted at various temperatures and extracellular Ca 2ϩ concentrations ([Ca 2ϩ ] o ). Recent studies (10, 11) have exploited the negative inotropic action (37) and cardioprotective properties (30) of the chemical agent 2,3-butanedione monoxime (BDM), whereas earlier studies utilized other forms of arrest.It ] o (9, 32), although Pinto and Patitucci (32) stated that temperature had little effect on the rate of creep of passive cardiac tissue. BDM has been reported to offer protection from cutting injury (30) and the Ca 2ϩ paradox (5), as well as from hypoxia and reperfusion injury (31). It also inhibits, but does not prevent, contracture (17).To ensure that cardiac muscle preparations are truly "passive," experiments have traditionally been conducted at low [Ca 2ϩ ] o and, for convenience, at room temperature. More recently, the use of BDM has further ensured passivity (10, 11); yet its effects on the mechanical properties of quiescent cardiac tissue at room temperature (20 -22°C) and low [Ca 2ϩ ] o have not been explored. At 26°C and 0.5 mM [Ca 2ϩ ] o , BDM was found to have no effect on the...

Energetics of stress production in isolated cardiac trabeculae from the rat

“…The lowest values of the dynamic modulus at 3 and 4 Hz were greater than those at lower stimulus frequencies. The measured magnitudes of dynamic moduli were in accord with reported values (25,26).…”

Biomechanical properties and microstructure of human ventricular myocardium

“…2. It is crucial to perform mechanical experiments on passive cardiac tissues at sufficient high temperatures (>25°C) or in the presence of an inhibitor of cross-bridge cycling, like BDM [38]. Additionally to CPS, the authors used both body temperature (37°C) and BDM to ensure passiveness of the cardiac muscle.…”

Comparison of Biomechanical Properties and Microstructure of Trabeculae Carneae, Papillary Muscles, and Myocardium in the Human Heart

“…The initial cross-sectional areas were computed as effective side lengths (distance between attachment points of two opposite sides) multiplied by average sample thickness [36]. Specimens were immersed in a bath of phosphate-buffered saline at 37 C throughout testing to maintain moisture and relax the myocytes [37].…”