Article Figures & Data
Figures
- Fig. 1.
PP2A-TG showed an increased relative heart weight (ordinate). Ordinate: relative heart weight (heart weight divided by body weight in milligrams per gram). WT, open circles; H2-TG, closed circles; PP2A-TG, squares; DT, triangles. Numbers in brackets indicate the numbers of animals investigated. +P ˂ 0.05 vs. WT.
- Fig. 2.
Ejection fraction (EF) of left ventricle after intraperitoneal injection of histamine or isoproterenol. Using echocardiography, histamine (100 µl of 1 mM, i.p.) elevated contractility in H2-TG compared with WT mice. PP2A-TG and DT (H2-TG × PP2A-TG) were less reactive to isoproterenol (100 µl of 10 mM, i.p.). Interestingly, in DT the EF was higher than in PP2A-TG at similar heart rates. ANOVA with Bonferroni post hoc test. +P ˂ 0.05 vs. WT, xP ˂ 0.05 vs. H2-TG, #P ˂ 0.05 vs. PP2A-TG, ⋆P ˂ 0.05 vs. corresponding basal level.
- Fig. 3.
(A) E′/A′ ratio in DT mice was increased. (B) Representative pulsed wave (PW) tissue Doppler of WT, which marks the S, E′, and A′ waves. S, systolic wave; E wave, mitral peak velocity blood flow in early diastole caused by left ventricular relaxation; A wave, peak velocity blood flow in late diastole caused by atrial contraction. By tissue Doppler, the retrograde waves, E' (passive LV filling) and A'-wave (atrial contraction) can be measured and E'/A' can be used as a marker of diastolic dysfunction, xP ˂ 0.05 vs. H2-TG. WT, open circles; H2-TG, closed circles; PP2A-TG, squares; DT, triangles.
- Fig. 4.
Overexpression of the catalytic subunit of PP2A in PP2A-TG led to increased systolic and diastolic diameters of the left ventricle. (A) Quantification of echocardiographically measured systolic or diastolic left ventricular (LV) diameters in parasternal long axis view (PLAX). DT (H2-TG × PP2A-TG) seemed to be less affected than PP2A-TG. ANOVA with Bonferroni post hoc test: +P ˂ 0.05 vs. WT, xP ˂ 0.05 vs. H2-TG, #P ˂ 0.05 vs. PP2A-TG. (B) Representative M-mode pictures for all investigated genotypes. Red, systolic diameter; blue, diastolic diameter.
- Fig. 5.
Typical original recordings of the time course of force reduction (no flow ischemia) and force recovery [reperfusion (Rep)] in isolated perfused heart (Langendorff) preparations from WT and H2-TG. The flow of 2 ml/min was stopped (global ischemia = no flow ischemia) for 20 minutes, as indicated by a horizontal line and restarted at the indicated time point. Ordinate: developed tension in millinewtons.
- Fig. 6.
A period of 20 minutes of ischemia (see Fig. 5) did not cause permanent damage because, after reperfusion, force (A) and heart rate (B) of both H2-TG and WT reached preischemic values again. Time to 50% decline of developed force (F1/2) during ischemia was reduced in H2-TG compared with WT (C), and after start of reperfusion, time to return to sinus rhythm was prolonged in H2-TG (*two of six preparations did not reach sinus rhythm within 15 minutes) compared with WT (D). Ctr, control perfusion without ischemia. +P < 0.05 vs. WT, n = 6.
- Fig. 7.
In vitro desensitization of H2-histamine receptors in isolated electrically driven (1 Hz) left atrial preparations of H2-TG mice. First (see schematic drawing), initial concentration-response curves for histamine or the H2-receptor agonist dimaprit were established. The effect of histamine was completely washed out by repeatedly exchanging the buffer in the organ bath. Thereafter, preparations were incubated with a high concentration of histamine or dimaprit (100 µM) for 1 hour, or no additions were given [nondesensitized (N-DS)]. After complete washout of histamine/dimaprit, a second concentration-response curve for (A) histamine or (C) dimaprit was obtained. (B) EC50 value of histamine; (D) comparison of desensitization (des.) with histamine and dimaprit. Similarly, as in left atria, desensitization was studied in isolated spontaneously beating right atrial preparations comparing histamine (E) and dimaprit (F) as histamine receptor agonists. The positive chronotropic effect (given as beating rate in the ordinates) of H2-receptor stimulation was subject to desensitization by both histamine and dimaprit. Ctr, control data before drug application. Numbers in brackets indicate animals studied. *First P ˂ 0.05 vs. Ctr; #P ˂ 0.05 vs. nondesensitized; +P ˂ 0.05 vs. desensitization with histamine. DS, desensitization.
- Fig. 8.
In vivo desensitization. Living H2-TG mice were treated intraperitoneally with dimaprit, and echocardiographic responses were studied. After recording basal cardiac parameters and dimaprit-induced cardiac effects, a high dose of dimaprit was injected [saline buffer in control experiments; nondesensitized (N-DS)], and 30 minutes later, dimaprit was injected again. Here, the effects of the third application of dimaprit are shown: (A) changes in heart rate after dimaprit injection and (B) changes in ejection fraction (EF) after dimaprit injection. *P ˂ 0.05 vs. N-DS. Hence, the contractile and chronotropic effects of dimaprit are attenuated after desensitization. DS, desensitization.
- Fig. 9.
Hypoxia in isolated electrically driven (1 Hz) left atrium in the organ bath. (A–D) Representative recordings of WT and H2-TG left atrial preparations demonstrate the experimental design of the study (left-hand sides of panels, respectively). In the diagrams, the force of contraction in % of control (Ctr = initial force at the beginning of the experiment) during the time of reoxygenation is presented. In H2-TG left atria, a better recovery was noted after a single hypoxia compared with WT (A). In presence of cimetidine (10 μM), this effect was absent (B). A preconditioning period (10 minutes of hypoxia) was not beneficial (C). In the presence of histamine (1 μM), the relative force during reoxygenation was greatly increased in H2-TG and reached again the initial force (D). Cim, cimetidine; His, histamine. *P < 0.05 vs. WT.
- Fig. 10.
Echocardiographic parameters under simulated sepsis. H2-TG and WT mice were injected with LPS or solvent control (NaCl). Data were collected before [basal (B)] as well as 1, 3, and 7 hours after LPS application. (A) Ejection fraction (EF) measured in the parasternal long-axis (PLAX) view; (B) heart rate; (C) pulmonary arterial flow; (D) cardiac output. Numbers in brackets indicate numbers of animals investigated. ANOVA with Bonferroni post hoc test: ⋆P < 0.05 vs. corresponding NaCl; #P < 0.05 vs. B.
- Fig. 11.
Scheme of a mammalian cardiomyocyte. Histamine in the extracellular space stimulates H2-histamine receptors (H2R). This can lead to increased activity of stimulatory GTP-binding proteins (Gs) and hence increased activity of the adenylyl cyclase (AC). This will increase the level of cAMP, which elevates the activity of cAMP-dependent protein kinases A (PKA). The kinases can increase the phosphorylation state (P) of cardiac regulatory proteins like the L-type calcium ion channel (LTCC), the ryanodine receptor (RyR) in the junctional sarcoplasmic reticulum, and PLB in the free sarcoplasmic reticulum. Phosphorylation of PLB increases the uptake of calcium ions (Ca2+) into the sarcoplasmic reticulum via sarcoplasmic reticulum ATPase (SERCA), where it binds mainly to calsequestrin (CSQ). Protein phosphatases like the catalytic subunit of PP2A (a serine, threonine phosphatase) reverse these phosphorylations. Increases in free cytosolic calcium ion concentrations due to H2-histamine receptor stimulation lead to an increase in force of contraction via action on myofibrils. Under pathophysiological conditions like sepsis, histamine levels can increase in the extracellular space and might desensitize histamine receptors. H2-histamine receptors are typically blocked by cimetidine. LPSs, mediators of bacterial sepsis, can decrease cardiac contractility via action on the toll like receptor 4 complex (CD14/TLR4) on cardiomyocytes and increased levels of cardiac depressant inflammatory mediators.
