Initial Characterization of Transgenic Mice Overexpressing Human Histamine H₂Receptors

Abstract

In an integrative approach, we studied the role of histamine H 2 receptors in the mouse heart. We noted that histamine, added cumulatively to the organ bath, failed to affect the force of contraction in left atrial preparations and did not change spontaneous heart rate in right atrial preparations from wildtype mice. By contrast, in the same preparations from mice that overexpressed the human H 2 receptor in a cardiac-specific way, histamine exerted concentration-and time-dependent positive inotropic and positive chronotropic effects. Messenger RNA of the human H 2 receptor was only detected in transgenic mice. Likewise, immunohistology and autoradiography only gave signals in transgenic but not in wild-type cardiac preparations. Similarly, a positive inotropic and positive chronotropic effect was observed with histamine in echocardiography of living transgenic mice and isolated perfused hearts (Langendorff preparation). Phosphorylation of phospholamban was increased in atrial and ventricular preparations from transgenic mice, but not in wild-type animals. The effects of histamine were mimicked by dimaprit and amthamine and antagonized by cimetidine. In summary, we generated a new model to study the physiologic and pathophysiologic cardiac role of the human H 2 receptor.

Phosphodiesterases 2, 3 and 4 can decrease cardiac effects of H2-histamine-receptor activation in isolated atria of transgenic mice

“…As in the present study and our earlier study (Gergs et al, 2019b), others noted that the combination of 300 nM cilostamide with 1 μM rolipram increased the beating rate in right atrial preparations of WT mice to a maximum, making it impossible to stimulate the beating rate further with isoprenaline (Galindo-Tovar and Kaumann, 2008). Galindo-Tovar et al (2009) argued that the lack of potentiation of the chronotropic effects of rolipram, cilostamide, and concurrent rolipram and cilostamide means that the cAMP pool governing H 2 -receptor-mediated sinoatrial tachycardia is protected from PDE3 and PDE4 and represents a compartment distinct from the cAMP compartment in which both PDE3 and PDE4 reduce basal sinoatrial beating.…”

“…Cilostamide and rolipram, administered together, caused marked increases in sinoatrial rate in isolated right atrium from WT mouse (Galindo-Tovar and Kaumann, 2008). In our previous work (Gergs et al, 2019b), and in the present work, an increase in the beating rate in WT or H 2 -TG right atria by cilostamide was not detected. Rolipram (1 μM) tended to transiently increase sinoatrial rate in isolated Kaumann, 2008).…”

“…However, this PIE can be disclosed by preincubation with cilostamide alone (in rat and man) and is even higher in the combined presence of cilostamide and rolipram (rat and man: Afzal et al, 2008, pig: Galindo-Tovar et al, 2009. It is noteworthy that in WT mice, neither cilostamide, nor rolipram, nor EHNA, nor their combinations, unveiled a PIE to 5-HT (Gergs et al, 2019b) or to histamine (this study).…”

“…In brief, right or left atrial preparations were isolated and mounted in organ baths as described by Gergs et al (2013Gergs et al ( , 2017Gergs et al ( , 2019b and Neumann et al (2003). The organ baths' bathing solution contained 119.8 mM NaCl 5.4 mM KCl, 1.8 mM CaCl 2 , 1.05 mM MgCl 2 , 0.42 mM NaH 2 PO 4 , 22.6 mM NaHCO 3 , 0.05 mM Na 2 EDTA, 0.28 mM ascorbic acid, and 5.05 mM glucose.…”

Initial Characterization of Stressed Transgenic Mice With Cardiomyocyte-Specific Overexpression of Protein Phosphatase 2C

“…To address the ventricular function in vitro , Langendorff perfusion experiments were performed as published before with slight modifications ( Gergs et al, 2019b ). In brief, spontaneously beating hearts were retrogradely perfused under constant flow (2 ml/min) and the force of contraction was measured mechanically at the apex of the heart.…”