Cell signaling of adjacent cells. In cardiac muscle, gap junctions between adjacent cells allows for action potential propagation from the cardiac pacemaker region of the heart to spread and coordinately cause contraction of the heart. The notch signaling mechanism is an example of juxtacrine signaling (also known as contact-dependent signaling) in which two adjacent cells must make physical contact in order to communicate. This requirement for direct contact allows for very precise control of cell differentiation during embryonic development. In the worm "Caenorhabditis elegans", two cells of the developing gonad each have an equal chance of terminally differentiating or becoming a uterine
Heart failure with preserved ejection fraction and lower ejection fractions. Cardiac output is dependent on stroke volume and heart rate. A significant portion (55-77%) of HFpEF patients are unable to increase heart rate to compensate for increased output demand (as in the setting of exercise); this is termed chronotropic incompetence. Combined with the characteristic deficit in stroke volume observed in HFpEF patients, many individuals display poor exercise tolerance. Non-simultaneous contraction of the left and right ventricle, dyssychrony, is present in up to 58% of HFpEF patients. However, dyssynchrony is also common in HFrEF and its role in HFpEF in particular remains obscure. While therapies for dyssynchrony,