Cellular basis of negative inotropic effect of 2,3-butanedione monoxime in human myocardium

Abstract

2,3-Butanedione monoxime (BDM) exerts a marked negative inotropic effect and has been shown to have protective actions on human myocardial force production that may be of clinical use. To determine the underlying mechanisms, we studied the effects of BDM on chemically skinned and aequorin-loaded myopathic human myocardium from transplant recipients. Eighteen muscles were chemically skinned with saponin (250 micrograms/ml) and then subjected to activation-relaxation cycles, with and without 5 mM BDM. Contracture force vs. Ca2+ data were fitted to a modified Hill equation, and values for 50% maximal activation (pCa50) and maximal Ca(2+)-activated force (Fmax) were obtained. pCa50 was decreased by 0.2 pCa units, indicating myofilament Ca2+ desensitization, and Fmax was reduced by 48% in 5 mM BDM. A second group of intact muscles (n = 8) was loaded with aequorin to monitor intracellular calcium (Cai2+) transients (peak light) and twitch force in the presence of BDM (1-30 mM). Over a range of 1-20 mM, BDM depressed peak light by 3-49% while force was depressed by 10-82%. This was accompanied by an abbreviation of the duration of the twitch but not of the Cai2+ transient. At a concentration of 30 mM, BDM completely inhibited force generation, but an Cai2+ transient was still present. We conclude that in human myocardium, 5 mM BDM predominantly affects cross-bridge force production and Ca2+ sensitivity and has a less pronounced effect on Cai2+.

Spontaneous calcium release in tissue from the failing canine heart

“…Despite the fact that numerous studies from both human (3,24) and animal (2, 22, 36) models of HF have attributed the mechanical dysfunction to changes in the calcium regulation observed in isolated myocytes (see Refs. 37 and 40 for reviews), few reports have made comparisons from intact tissue (16,21,23,25,34). We found in canine tachycardia-induced HF that calcium transient amplitude is reduced and the duration is prolonged compared with normal.…”

2,3-Butanedione Monoxime Suppresses Primarily Total Calcium Handling in Canine Heart.

“…Working points away from this encircled area on the BDM N-R line as well as the control N-R line requires futile Ca 2ϩ cycling (NϾ0) and R values greater than 0.15. However, no data exists in literature [1][2][3][4][5][6][7][8][9][10][11][12] to suggest that BDM increases R (i.e., the reactivity of E max to total Ca 2ϩ handling). Therefore, a reasonable working point under BDM cannot exist on the BDM (dashed) N-R lines except where the R-axis intercepts within the same shaded rectangle in Fig.…”

“…Some studies indicate that BDM suppresses primarily crossbridge force development without suppressing intracellular Ca 2ϩ transient in the myocardium [6][7][8]. Other reports indicate that BDM suppresses simultaneously or even primarily the Ca 2ϩ influx as well as the Ca 2ϩ store in the sarcoplasmic reticulum (SR) and its release in the myocardium [9][10][11][12].…”

“…Other reports indicate that BDM suppresses simultaneously or even primarily the Ca 2ϩ influx as well as the Ca 2ϩ store in the sarcoplasmic reticulum (SR) and its release in the myocardium [9][10][11][12]. However, their relative contributions to depressed contractility are still controversial in the mammalian (including human) myocardium [1][2][3][4][5][6][7][8][9][10][11][12].…”

Calpain-Mediated Impairment of Na + /K + –ATPase Activity During Early Reperfusion Contributes to Cell Death After Myocardial Ischemia

“…Through these mechanisms, BDM reduces cross-bridge force production and allows a complete blockade of contractile activity. 34 BDM has been consistently shown to prevent hypercontracture and sarcolemmal rupture during the initial minutes of reperfusion. 1,2,35,36 Hearts reperfused for 5 minutes in the presence of BDM, in which LDH release and contraction band necrosis were importantly reduced, showed calpain activation, reduction of Na ϩ /K ϩ -ATPase activity, and loss of anchorage of ␣ subunits …”