Myocardial to Endocardial Commuication


Endocardial cells combine to form endocardium tissues and are the inner-most layer of tissues that line the chambers of the heart. These tissues play a role in controlling myocardial contractions in mammals.


Endocardial notch signaling is one of several forms of communication utilized by endocardial cells to communicate with each other. It is a highly conserved cell signaling system meaning that the both the nucleic acid and protein sequences are similar and in some cases are even identical in different species of organisms.

There are four different notch receptors: NOTCH 1, NOTCH 2, NOTCH 3, and NOTCH 4. The notch signaling system also includes notch ligands that act as the receptors. These ligands are transmembrane receptor proteins that span the length of the membrane of the endocardial cell. The notch signaling receptor is a heterodimer transmembrane protein, meaning that the protein was formed from the combination of two normally non-covalently bonded macromolecules.

Notch signaling is activated by cell to cell contact causing the ligand to bind to the notch receptor. When this signal is activated it leads to three cleavages. The first cleavage is activated by an enzyme known as TACE/ADAM17 and this is responsible for the cleavage of the membrane. The other two cleavages are controlled by a mixture of enzyme (presenilin1, presenilin2, Pen-2, Aph-1, and nicastrin).

This form of signaling allows a group of cells to arrange themselves to form a large structure by influencing them to switch off certain traits in neighbouring cells.


Cell adhesion also occurs in endocardial cells.

The endocardial cell is structural made of 5-6 cubular cells along the AP axis of the endocardiaum (Westerfield et al 2009). The endocardial cell migrate mid-line before myocardial cells. Preceding myocardial cell bilateral migration, localized cardiomycytes change direction. This causes myocardial cells to alter direction and move inward to meet the endocardial cells thus establishing nascent heart circumference. Bilateral heart fields are formed as a result of fusion at the midline between the two forming cardiac tissue discs, which are located at the central circumference of the future ventricle (Bakkers 2011).

The physical proximity of the endocardial and myocardial cell suggests that the two may be influenced by each other or that they both respond to the similar environmental cues during their migration towards the midline. One such non-cardiac tissue to which both myocardial and endocardial cells are enar is the endoderm. The endoderm, which will later form the gut is shown to be an influencing factor in cardiac fusion.

1.Monte Westerfield, Leonard I. Zon, H. William Detrich, III ‘Essential Zebrafish Methods’. 2009.

1. Monte Westerfield, Leonard I. Zon, H. William Detrich, III ‘Essential Zebrafish Methods’. 2009.


Monte Westerfield, Leonard I. Zon, H. William Detrich, III ‘Essential Zebrafish Methods’. 2009.

Jeroen Bakkers. ‘Zebrafish as a model to study cardiac development and human cardiac disease

Received January 18, 2011.

Revision received March 22, 2011.

Accepted April 1, 2011,_notch

Myocardial Communication at its Best!

Myocardial cells communicate using autocrine factors, cell to cell propagation of depolarization fronts, gap junctions and adhesion complexes. The autocrine communications involved an abundant array of secretions from leptin, FGF and TGFβ family members, midkine, hepatocyte growth factor, endothelin-1, and stromal cell–derived factor 1α, which causes the myocardial cell communications.

Adhesion complexes engage in cell to cell communication with intracellular signaling that are activated by cell to cell or cell to matrix action of specific protein in the complexes. This signal results in in the myocardial reactions to growth being changed to control cardiac development and hypertrophy.


Intercalated discs are made up of two types of cell junctions: desmosomes and gap junctions. Desmosomes comprises of strong protein fibers that are very tough and securely connects the myocardial cells together. This is a significant characteristic because of the continuous pumping of the heart results in an immense amount of pressure for the networks between the cells. Myocardial cells are stimulated to create electric current that can instigate and transmit action potentials. The transmission of action potential from one myocardial cell to another myocardial cell follows the transfer of sodium ions across the gap junction or can be referred to as an electric synapse.  Gap junctions connect the cytoplasm of a cell to bordering cells by small linking tubes called connexins, which allows miniature molecules and ions to easily move from one myocardial cell to another. Myocardial cells are branched and joined with other myocardial cells hence together with the gap junctions at the intercalated discs, an high intensity of correlations between the myocardial cells are produced. The myocardial cells linked to the gap junctions are all together known as a myocardium which functions as one. The entire myocardium contracts together when it is stimulated.

myocardial cell

“Cell Communications in the Heart .” Circulation . Accessed October 18, 2013.

A myocardium is made up of two ventricles and another myocardium is from by two atria. The ventricles and the atria are dived by non-conducting fibrous skeleton. The simultaneous contraction of the myocardial cells which comprises the myocardium is essential to generate the force vital to allow pumping of blood.


“Cell Communications in the Heart .” Circulation . Accessed October 18, 2013.

Poon, Kar Lai , and Thomas Brand. “The zebrafish model system in cardiovascular research: A tiny fish with mighty prospects.” Global Cardiology Science & Practice 4 (2013).Accessed October 14, 2013 10.5339/gcsp.2013.4 .

Affairs of the Heart

I have chosen to reside in the heart of the zebrafish as a myocardial cell. I was born from a stem cell which added a special touch (specialization of cells). Stem cells are non-specialized cell that undergo complex processes, both during embryonic and adult life. Mitosis causes the segregation of cells followed by the specialization of the cells, i.e. the cells get assigned functional roles in the zebrafish.  

The heart is a vital organ in any organism as it works in a transport system, where blood is carried throughout the body providing oxygen and sustenance to other cells of the body as well as ridding the body of waste products such as carbon dioxide. The heart is the first organ to function during the embryo development.

Heart muscle cells (shown in green), regress to a more youthful state after injury, start dividing again (indicated by a red marker) to replenish lost cells and then mature a second time into cardiomyocytes.

Structure of myocardial cell in the zebrafish

I have one oval/circular shaped nucleus which is responsible for the controlling my every action, such as reproduction, metabolism and growth. Therefore you can say the nucleus is like my brain. I also have DNA which allows my offspring to function exactly like me. My nucleus is well protected as it is membrane bound, just as the brain is protected by the skull.

I also have lots of energy to perform all my duties, the contracting and relaxing is quite exhausting you know. And I would like to thank the mitochondria in me that provide me with lots of ATP that get me through this active life. This to, is well protected as it is membrane bound.

I have myofibrils which is just contractile protein fibers that are elongated and in abundance. Honestly I just think they are to make me look buffJ. Unlike my other organelles the myofibrils are not membrane bound.

I don’t have much organelles, you know, because of my duty, which just requires lots of energy. But a very cool thing is I can aid in the regeneration of the heart organ (I would tell u more about this a next time).

My main purpose in life is to work alongside my brothers and sisters (other myocardial cells) that make up the cardiac muscle. Together we are responsible for the heartbeat of the zebrafish and the functioning of the cardiovascular system.


Zebrafish heart