Jürgen Heubach | Search PubMed

PubMed2004

Beta adrenergic receptor-mediated atrial specific up-regulation of RGS5.

Previous investigations had suggested that signaling from the overexpressed beta(2) adrenergic in the heart of transgenic TG4 mice was dampened in the atria. Using an RT-PCR based strategy, we have identified Regulator of G-protein Signaling 5 (RGS5) as being up-regulated in the atria of TG4 mice. Northern blot analysis demonstrated that RGS5 levels were 3 fold higher in the atria of TG4 mice. Western blot analysis of a panel of rat tissues demonstrated that basal expression of RGS5 protein was confined to the heart and skeletal muscle. Furthermore, RGS5 protein was detected in skeletal muscle C2C12 and cardiomyocyte HL-1 cultured cell lines. As observed for RGS5 mRNA levels in TG4 mice, RGS5 protein levels were increased in the atria of rats that were administered the beta adrenergic agonist isoproterenol during a 14 day period. Taken together, these results indicate that RGS5 is a housekeeping RGS in the heart and in skeletal muscle while its beta adrenergic-mediated induction in the atrium suggests that it also has a highly specialized function.

Adrenergic beta-Agonists↗

PubMed2002

Cardiac tissue engineering.

Recent progress in implantations of differentiated cardiac and non-cardiac cells as well as adult stem cells into the heart suggests that the irreversible loss of viable cardiac myocytes that occurs during myocardial infarction can be at least partly substituted. We evaluated an alternative approach by reconstituting cardiac tissue grafts in vitro and implanting them as spontaneously and coherently contracting tissues. For this purpose we have optimized a method to generate ring-shaped three-dimensional engineered heart tissue (EHT) in vitro from neonatal rat cardiac myocytes. When subjected to isometric force measurements in organ baths, electrically stimulated EHTs exhibit a Frank-Starling behavior, a positive inotropic response to increases in extracellular calcium, a positive inotropic and lusitropic response to isoprenaline, and a negative inotropic response to the muscarinic agonist carbachol ('accentuated antagonism'). Twitch tension under maximal calcium amounts to 1-2 mN/ mm2. Importantly, passive (resting) tension is low, yielding a ratio of active/passive tension of approximately 1.5 under basal and 14 under maximal calcium. Morphologically, EHTs represent a highly interconnected three-dimensional network of cardiac myocytes resembling loose cardiac tissue with a high fraction of binucleated cardiac myocytes, strong eosin staining and elongated centrally located nuclei. Electron microscopy demonstrated well developed sarcomeric structures, T-tubules, SR vesicles, T-tubule-SR-junctions, all types of intercellular connective structures, and a basement membrane. Thus, EHTs comprise functional and morphological properties of intact, ventricular myocardium. First implantation experiments of EHTs in the peritoneum of Fischer 344 rats showed that EHTs survived for at least 14 days, maintained a network of differentiated cardiac myocytes, and were strongly vascularized. Thus, EHTs may serve as material for a novel tissue replacement approach.

Animals↗