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Two subtypes of ␤-adrenoceptors, ␤1 and ␤2, mediate cardiac catecholamine effects. These two types differ qualitatively, e.g., regarding G protein coupling and calcium channel stimulation. Transgenic mice overexpressing human ␤2-adrenoceptors survive high-expression levels, unlike mice overexpressing ␤1-adrenoceptors. We examined the role of inhibitory Gi proteins, known to be activated by ␤2-but not ␤1-adrenoceptors, on the chronic effects of human ␤2-adrenoreceptor overexpression in transgenic mice. These mice were crossbred with mice where G␣i2, a functionally important cardiac Gi ␣-subunit, was inactivated by targeted gene deletion. Survival of ␤2-adrenoreceptor transgenic mice was reduced by heterozygous inactivation of G␣i2. Homozygous knockout͞␤2-adrenoreceptor transgenic mice died within 4 days after birth. Heterozygous knockout͞␤2-adrenoreceptor transgenic mice developed more pronounced cardiac hypertrophy and earlier heart failure compared with ␤2-adrenoreceptor transgenic mice. Single calcium-channel activity was strongly suppressed in heterozygous knockout͞␤2-adrenoreceptor transgenic mice. In cardiomyocytes from these mice, pertussis toxin treatment in vitro fully restored channel activity and enhanced channel activity in cells from homozygous G␣i2 knockout animals. Cardiac G␣i3 protein was increased in all G␣i2 knockout mouse strains. Our results demonstrate that G␣i2 takes an essential protective part in chronic signaling of overexpressed ␤2-adrenoceptors, leading to prolonged survival and delayed cardiac pathology. However, reduction of calcium-channel activity by ␤2-adrenoreceptor overexpression is due to a different pertussis-toxin-sensitive pathway, most likely by G␣i3. This result indicates that subtype-specific signaling of ␤2-adrenoreceptor functionally bifurcates at the level of Gi, leading to different effects depending on the G␣ isoform.L-type calcium channel ͉ single channel recording ͉ mouse genetics ͉ survival curve ͉ pertussis toxin C ardiac stimulatory catecholamine effects are mediated by both ␤ 1 -and ␤ 2 -adrenergic receptors (␤-adrenoceptors), mainly through cAMP-dependent protein kinase A-catalyzed phosphorylation of cardiac proteins involved in calcium homeostasis, such as phospholamban and the L-type calcium channel. Evidently, this pathway is compromised in heart failure. Because of the clear-cut evidence that ␤ 2 -adrenoceptors mediate acute functional effects in human cardiomyocyte in vitro (1, 2) and in vivo (3), a rationale for ␤ 2 -adrenoreceptor gene therapy exists (4-6). Whether and where ␤ 2 -adrenoreceptor stimulation or inhibition, by pharmacological or genetic means, will have its place in heart failure therapy is an open question (7-9).Inherent in the clinical discussion is recent molecular insight into differences between cardiac ␤ 1 -and ␤ 2 -adrenoreceptor stimulation at the signal-transduction level (10, 11). In rat cardiomyocytes, a ␤ 2 -agonist, zinterol, was shown to increase calcium current in a manner qualitatively distinct from ␤ 1 -adrenoreceptor stimu...

Various strategies have been published enabling cardiomyocyte differentiation of human induced pluripotent stem (iPS) cells. However the complex nature of signaling pathways involved as well as line-to-line variability compromises the application of a particular protocol to robustly obtain cardiomyocytes from multiple iPS lines. Hence it is necessary to identify optimized protocols with alternative combinations of specific growth factors and small molecules to enhance the robustness of cardiac differentiation. Here we focus on systematic modulation of BMP and WNT signaling to enhance cardiac differentiation. Moreover, we improve the efficacy of cardiac differentiation by enrichment via lactate. Using our protocol we show efficient derivation of cardiomyocytes from multiple human iPS lines. In particular we demonstrate cardiomyocyte differentiation within 15 days with an efficiency of up to 95 % as judged by flow cytometry staining against cardiac troponin T. Cardiomyocytes derived were functionally validated by alpha-actinin staining, transmission electron microscopy as well as electrophysiological analysis. We expect our protocol to provide a robust basis for scale-up production of functional iPS cell-derived cardiomyocytes that can be used for cell replacement therapy and disease modeling.Electronic supplementary materialThe online version of this article (doi:10.1007/s12015-014-9564-6) contains supplementary material, which is available to authorized users.

BackgroundIncreased activity of single ventricular L-type Ca2+-channels (L-VDCC) is a hallmark in human heart failure. Recent findings suggest differential modulation by several auxiliary β-subunits as a possible explanation.Methods and ResultsBy molecular and functional analyses of human and murine ventricles, we find that enhanced L-VDCC activity is accompanied by altered expression pattern of auxiliary L-VDCC β-subunit gene products. In HEK293-cells we show differential modulation of single L-VDCC activity by coexpression of several human cardiac β-subunits: Unlike β1 or β3 isoforms, β2a and β2b induce a high-activity channel behavior typical of failing myocytes. In accordance, β2-subunit mRNA and protein are up-regulated in failing human myocardium. In a model of heart failure we find that mice overexpressing the human cardiac CaV1.2 also reveal increased single-channel activity and sarcolemmal β2 expression when entering into the maladaptive stage of heart failure. Interestingly, these animals, when still young and non-failing (“Adaptive Phase”), reveal the opposite phenotype, viz : reduced single-channel activity accompanied by lowered β2 expression. Additional evidence for the cause-effect relationship between β2-subunit expression and single L-VDCC activity is provided by newly engineered, double-transgenic mice bearing both constitutive CaV1.2 and inducible β2 cardiac overexpression. Here in non-failing hearts induction of β2-subunit overexpression mimicked the increase of single L-VDCC activity observed in murine and human chronic heart failure.ConclusionsOur study presents evidence of the pathobiochemical relevance of β2-subunits for the electrophysiological phenotype of cardiac L-VDCC and thus provides an explanation for the single L-VDCC gating observed in human and murine heart failure.

L-type calcium channels are composed of a pore, alpha1c (Ca(V)1.2), and accessory beta- and alpha2delta-subunits. The beta-subunit core structure was recently resolved at high resolution, providing important information on many functional aspects of channel modulation. In this study we reveal differential novel effects of five beta2-subunits isoforms expressed in human heart (beta(2a-e)) on the single L-type calcium channel current. These splice variants differ only by amino-terminal length and amino acid composition. Single-channel modulation by beta2-subunit isoforms was investigated in HEK293 cells expressing the recombinant L-type ion conducting pore. All beta2-subunits increased open probability, availability, and peak current with a highly consistent rank order (beta2a approximately = beta2b > beta2e approximately = beta2c > beta2d). We show graded modulation of some transition rates within and between deep-closed and inactivated states. The extent of modulation correlates strongly with the length of amino-terminal domains. Two mutant beta2-subunits that imitate the natural span related to length confirm this conclusion. The data show that the length of amino termini is a relevant physiological mechanism for channel closure and inactivation, and that natural alternative splicing exploits this principle for modulation of the gating properties of calcium channels.

The trials performed to date to addressing the effect of SDM on patient-relevant, disease-related endpoints are insufficient in both quantity and quality. Although just under half of the trials reviewed here indicated a positive effect, no final conclusion can be drawn. A consensus-based standardization of both SDM-promoting measures and appropriate clinical studies are needed.

Autism Spectrum Disorders (ASD) are complex neurodevelopmental diseases clinically defined by dysfunction of social interaction. Dysregulation of cellular calcium homeostasis might be involved in ASD pathogenesis, and genes coding for the L-type calcium channel subunits CaV1.2 (CACNA1C) and CaVβ2 (CACNB2) were recently identified as risk loci for psychiatric diseases. Here, we present three rare missense mutations of CACNB2 (G167S, S197F, and F240L) found in ASD-affected families, two of them described here for the first time (G167S and F240L). All these mutations affect highly conserved regions while being absent in a sample of ethnically matched controls. We suggest the mutations to be of physiological relevance since they modulate whole-cell Ba2+ currents through calcium channels when expressed in a recombinant system (HEK-293 cells). Two mutations displayed significantly decelerated time-dependent inactivation as well as increased sensitivity of voltage-dependent inactivation. In contrast, the third mutation (F240L) showed significantly accelerated time-dependent inactivation. By altering the kinetic parameters, the mutations are reminiscent of the CACNA1C mutation causing Timothy Syndrome, a Mendelian disease presenting with ASD. In conclusion, the results of our first-time biophysical characterization of these three rare CACNB2 missense mutations identified in ASD patients support the hypothesis that calcium channel dysfunction may contribute to autism.

Limited access to expert tutors is a problem that can be addressed by using tutors from different stages of medical or non-medical (under-, post-) graduate education. To address whether such differences in qualification affect the results of process evaluation by participants or their learning outcome (exam results), we analysed the data of a 4-year prospective study performed with 787 3rd-year medical students (111 groups of 5-10 participants) taking an obligatory problem-based learning (PbL)-course of basic pharmacology. We compared peer tutors (undergraduate medical students, >/=4th year), non-expert (junior) staff tutors (physicians, pharmacists, veterinarians, biologists, or chemists during postgraduate education), and expert (senior) staff tutors (completed postgraduate education). Evaluation scores related to PbL gave the highest values for senior staff-led groups. The tutor's performance score of peer-led groups did not differ from those of staff-led groups, but the score obtained from groups tutored by junior staff was lower than that obtained with senior staff tutors. Students' weekly preparation time tended to be lower in peer-led groups, while learning time spent specifically on exam preparation seemed to be increased compared to PbL-groups of staff tutors. As a putative confounding variable, tutors' experience in coaching PbL-groups was also investigated. Groups led by experienced tutors, defined as tutors with at least one term of previous PbL tutoring, were found to have significantly higher evaluation scores. Interestingly, neither tutors' subject-matter expertise (peer students, junior staff, or senior staff) nor their teaching-method expertise showed any influence on PbL-groups' mean test scores in a written exam. This indicates that the effect of tutor expertise on the learning process is not associated with a difference in learning outcome when just factual knowledge is assessed by traditional methods.