Temperature alters the inotropic, chronotropic and proarrhythmic effects of histamine in atrial muscle preparations from humans and H2-receptor overexpressing mice

Fig. 1. A Scheme. Histamine can stimulate H2-receptors in cardiomyocytes from H2-TG mice. This leads via stimulatory GTP binding proteins (Gs) to enhanced formation of cAMP by adenylyl cyclase (AC) in the sarcolemma. Produced cAMP then can activate protein kinase (PKA) which usually enhances the activity of regulatory proteins. For instance, enhanced phosphorylation of the inhibitory subunit of troponin (TnI) leads to more rapid relaxation of the heart, whereas enhanced phosphorylation of the L-type Ca2+ current (LTCC) leads to increased Ca2+ inflow into the cell. This Ca2+ can release Ca2+ by action on the ryanodine receptor (RyR in the sarcoplasmic reticulum). Release of Ca2+ is increased by phosphorylation of RyR. Relaxation is also enhanced by phosphorylation of phospholamban (PLB) which activates SERCA and thereby promotes removal of Ca2+. From the vicinity of myofilaments into the sarcoplasmic reticulum. Enhanced entrance of sodium via a sodium channel (Na+) can elevate intracellular sodium which can be extruded via the sodium calcium exchanger NCX. Finally, the cell can depolarize and early (EAD) and late afterdepolarization (DAD) could occur manifesting itself as arrhythmias. B…

Fig. 2. Histamine increases force of contraction in human atrial preparations in a concentration dependent manner. A Original recordings of CRC’s in human atrial preparations at the different temperatures (37 °C, 23 °C and 42 °C). Ordinates in A and B depict developed force of contraction in milli Newton (mN). Ctr (control) indicates force before any drug application. Ordinate in C depicts normalized force: the maximum effect for each concentration response curve is arbitrarily set at 100% and the basal force is set at 0%. Abscissae show negative logarithmic concentrations of histamine. Temperatures of the organ baths are indicated as filled circles (37 °C), filled triangles with tip down (23 °C) or triangles with tip up (42 °C). “n” indicates the numbers of experiments. *: first p < 0.05 vs. Ctr., + : p < 0.05 vs. 37 °C ANOVA Dunnett

Fig. 3. Histamine increases the rate of tension development. Concentration response curves for histamine in human atrial preparation. C: dF/dt max and dF/dt min in milli Newton per second (A): time to peak tension (t1 in ms) and (B): relaxation time (t2 in ms) in electrically driven (1 Hz) right atrial preparations. Abscissae show negative decadic logarithmic concentrations of histamine. Temperatures of the organ baths are indicated as filled circles (37 °C), filled triangles with tip down (23 °C) or triangles with tip up (42 °C). “n” indicates the numbers of experiments. *: first p < 0.05 vs. Ctr., + : p < 0.05 vs. 37 °C ANOVA Dunnett, #: p < 0.05 vs. 23 °C ANOVA Dunnett

Fig. 4. Histamine increases force of contraction in H2-TG. A Original recordings of effect of increasing concentrations of histamine on electrically stimulated left atrial preparations from H2-TG. Concentration dependent effect of histamine on force of contraction. Ordinates in A and B depict developed force of contraction in milli Newton (mN). Ctr (control) indicates force before any drug application. Abscissae show increasing logarithmic concentrations of histamine. Temperatures of the organ baths are indicated as filled circles (37 °C), filled triangles with tip down (23 °C) or triangles with tip up (42 °C). “n” indicates the numbers of experiments. *: first p < 0.05 vs. Ctr., + : p < 0.05 vs. 37 °C ANOVA Dunnett, #: p < 0.05 vs. 23 °C ANOVA Dunnett

Fig. 5. Histamine increases the rate of tension development in left atrium. Concentration response curves for histamine in mouse atrial preparations. C, D dF/dt max and dF/dt min in milli Newton per second in H2-TG (C) or WT (D), respectively. A Time to peak tension (t1 in ms) and (B) relaxation time (t2 in ms) in electrically driven (1 Hz) left atrial preparations. Abscissae show increasing logarithmic concentrations of histamine. Temperatures of the organ baths are indicated as filled circles (37 °C), filled triangles with tip down (23 °C) or triangles with tip up (42 °C). “n” indicates the numbers of experiments. *: first p < 0.05 vs. Ctr., + : p < 0.05 vs. 37 °C ANOVA Dunnett, #: p < 0.05 vs. 23 °C ANOVA Dunnett

Fig. 6. Histamine increases the beating rate and the force of contraction in right atrium. Concentration response curves for histamine in spontaneously beating mouse right atrial preparations. A Original recordings of effect of increasing concentrations of histamine in the beating rate, B beating rate in beats per minute (BPM), C force of contraction in milli Newton. Abscissae show increasing logarithmic concentrations of histamine. Temperatures of the organ baths are indicated as filled circles (37 °C), filled triangles with tip down (23 °C) or triangles with tip up (42 °C). “n” indicates the numbers of experiments. *: first p < 0.05 vs. Ctr., + : p < 0.05 vs. 37 °C ANOVA Dunnett, #: p < 0.05 vs. 23 °C ANOVA Dunnett

Fig. 7. Hyperthermia and hypothermia reduce the effect of histamine on tension development in right atrial preparations. C, D dF/dt max and dF/dt min in milli Newton per second in H2-TG (C) or WT (D), respectively. A Time to peak tension (t1 in ms) and B relaxation time (t2 in ms) in spontaneously beating right atrial preparations. Abscissae show increasing logarithmic concentrations of histamine. Temperatures of the organ baths are indicated as filled circles (37 °C), filled triangles with tip down (23 °C) or triangles with tip up (42 °C). “n” indicates the numbers of experiments. *: first p < 0.05 vs. Ctr., + : p < 0.05 vs. 37 °C ANOVA Dunnett, #: p < 0.05 vs. 23 °C ANOVA Dunnett

Fig. 8. The effect of histamine on phosphorylation of phospholamban is temperature dependent. A. B Right-hand side: original Western blots: height of samples is given in kDA by arrows for protein markers. Western blots depicting expression serine 16 phosphorylated phospholamban and calsequestrin (CSQ) as loading control in wild type (WT) and H2-TG (TG) hearts are shown. The human control samples (Ctr) were treated with isoprenaline. Expression data were quantified and normalized to CSQ expression (ordinates). Temperatures of the organ baths are indicated as white bars (37 °C), dotted bars (23 °C) and dashed bars (42 °C). “n” indicates the numbers of experiments. *p < 0.05 vs. 37 °C

Fig. 9. Hyperthermia leads to arrhythmias. Occurrence of arrhythmias during at the indicated temperatures in right atrial preparations from WT and H2-TG mice. A Original recordings of right atrial preparations from WT (A) and H2-TG (B) mice during hyperthermia protocol. B Temperature-dependent average duration of arrhythmias during histamine addition in WT (white bar) and H2-TG (dashed bar). Ordinate depicts the time in seconds and the abscissa shows the different temperatures. “n” indicates the numbers of experiments. *p < 0.05 vs. 37 °C. + p < 0.05 vs. WT. C Temperature-dependent incidences of arrhythmias during histamine addition in WT (horizontal and vertical dashed bars) and H2-TG (diagonal dashed bars). Ordinate shows the incidences of the arrhythmias. The number of experiments were n = 16. *p < 0.05 (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\chi }^{2}$$\end{document}χ2-test)