C. Hernández-‐Sánchez, P. Vázquez, FloradePablo
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We set out, then, to demonstrate the presence of receptors which may
mediate theactionof catecholamines, likelyproducedby thecardiomyocytesof the
primitive heart tube.
Adrenergic and dopaminergic receptors are 7-‐
transmembrane domain G protein-‐coupled receptors. The family of adrenergic
receptors are composedbyα-‐ andβ-‐receptors. Thereare two typesof α-‐receptors:
Thestimulationof α-‐1-‐receptors (α-‐1a, α-‐1bandα-‐1dsubtypes) activates theGαq
subunit of Gproteins and, therefore, Phospholipase C is activated. In contrast, the
α-‐2-‐receptors (α-‐2a, α-‐2b, and α-‐2c subtypes) are coupled to Gαi/o subunit and,
therefore, inactivate adenyl cyclase (AC). In contrast, the β-‐adrenergic-‐receptors
family includes three subtypes: β-‐1, β-‐2, β-‐3, which activate the subunit Gαs and
subsequently increase the intracellular cAMP levels. However, the β-‐2 adrenergic
receptorsmayactivate theGαi andGβγsubunitsofGprotein insomecases.
The dopaminergic receptors are clasified into two subfamilies. The D1-‐
receptors (D1, D5) are coupled to Gαs proteins and their activation leads to
estimulation of AC and subsequent increase in cAMP levels. On the contrary, the
D2-‐receptors (D2, D3, D4) are coupled toGαi proteins and their activation leads to
inhibitionof ACanddecreaseof cAMP levels.Members of theD1andD2 receptors
can formheterodimers that are coupled toGαqproteins and their activation leads
tostimulationof phospholipaseCand intracellular calciumrelease.
Our preliminary studies showed the presence of adrenergic (both α and β
types) and dopaminergic receptors (D1 and D2 subfamilies) in the heart tube
(Figure 6) suggesting that catecholamines have the possibility to act through
them. Further studies are needed to confirm the role of the specific receptor
subtypesandsignalingpathways incardiogenesis.
4. L-‐DOPAANDDOPAMINE INDUCECARDIACDIFFERENTIATION
Differentiation of contracting cardiomyocyte requires the action of a
combination of transcription factors, includingNkx2.5 andTbx5 (17). The pattern
of th expression suggested that catecholamines may play a role in cardiac
development. Implantingmicrobeads soaked inL-‐DOPAanddopamine, laterally to
oneof thebilateral heart fields inculturedchickembryos,wecouldshowthat both
L-‐DOPAanddopamine induce cardiacmuscledifferentiation. Cardiac transcription
factors Nkx2.5 and Tbx5were expressed in the ectopic tissue generated near the
microbead (Figure7A). Additionally, the sarcomericproteinAMHC1 (atrialmyosin
heavy chain), marker of terminal cardiac differentiation, was also induced, as
reflectedby insituhybridizationand immunostainingwithMF20antibody (Figure
7A). Moreover, the cells of the induced ectopic tissue developed myofibrils
organized into sarcomeres, similar to those found in the cardiomyocytes of the
primitiveheart tube (Figure7B). The linkofTHtocardiacdifferentiationprograms
