These data reveal a previously unrecognized role for Wnt/Ca 2+ signalling in establishing an electrical gradient in the plane of the developing cardiac epithelium through modulation of ion-channel function. Although the traditional planar cell polarity pathway is not involved, we obtained evidence that Wnt11 acts to set up this gradient of electrical coupling through effects on transmembrane Ca 2+ conductance mediated by the L-type calcium channel. We excluded a role for differences in cellular excitability, connexin localization, tissue geometry and mechanical inputs, but in contrast we were able to demonstrate that non-canonical Wnt11 signals are required for the genesis of this myocardial electrical gradient. Here we identify a gradient of electrical coupling across the developing ventricular myocardium using high-speed optical mapping of transmembrane potentials and calcium concentrations in the zebrafish heart. The fundamental mechanisms that regulate the establishment and maintenance of such electrical polarities are poorly understood. When an ion moves along this path, down its electrochemical gradient, energy is freed that can then power diverse biological processes.Electrical gradients are critical for many biological processes, including the normal function of excitable tissues, left-right patterning, organogenesis and wound healing. It is the combined action of these electrical and chemical factors that determine the ultimate direction of an electrochemical gradient. The electrical gradient of a positively-charged ion flows from positive to negative regions, while the reverse is true for negatively-charged ions. In contrast, the electrical gradient revolves around an ion’s electrical charge and the overall charges of the intracellular and extracellular environments. The chemical gradient relies on differences in the abundance of a substance on the outside versus the inside of a cell and flows from areas of high to low ion concentration. However, energy can also be stored in the electrochemical gradient of an ion across the plasma membrane, which is determined by two factors: its chemical and electrical gradients. Generating energy for processes like glucose transport and providing a means for specialized cells such as cardiac, muscle and neurons to generate electrical impulses.Īdenosine triphosphate, or ATP, is considered the primary energy source in cells. The prevalence of positively charged sodium ions outside of the cell and the abundance of negative charged proteins inside are two major factors that contribute to the overall difference in charge across the membrane.Īctive transport uses energy to maintain the electrochemical gradient across the cell membrane with specialized membrane proteins moving ions against their electrochemical gradients. Under specific conditions however, the ions are allowed to move with their gradients.
The separation of ions and molecules with positive and negative charges also means that there is an electrical gradient present. The direction of electric field is in the direction of decreasing potential. Its easier to determine electric field from electric potential. The quantity V V is called potential gradient. However, ion concentration is not the only factor creating a gradient across the cell membrane. The gradient operator is (i dx + j dy + k dz) ( i d x + j d y + k d z). So its chemical gradient is in opposition to sodium's gradient. Conversely, there is a lower concentration of potassium outside of the cell and more potassium inside. This creates a chemical or concentration gradient where sodium would flow across the cell membrane from outside to inside if it were given a path. Under normal conditions there is generally more sodium on the outside of a cell than inside. Ions that are critical for cell function including sodium and potassium are unable to diffuse across the membrane relying instead on movement by channels and transporters. One feature of this division of resources inside and outside of the cell is the maintenance of an electrochemical gradient. Keeping some molecules and ions trapped within a cell while keeping others out. The cell membrane functions as a barrier.
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