Posts tagged nerve impulse
Articles and news from the latest research reports.
Researchers Reveal a New Pathway Through the Sodium Pump
A study in The Journal of General Physiology provides new evidence that the ubiquitous sodium pump is more complex—and more versatile—than we thought.
(Image caption: Structure of the sodium pump, which researchers reveal to be more versatile than previously thought)
The sodium pump is present in the surface membrane of all animal cells, using energy derived from ATP to transport sodium and potassium ions in opposite directions across the cell boundary. By setting up transmembrane gradients of these two ions, the pump plays a vital role in many important processes, including nerve impulses, heartbeats, and muscular contraction.
Now, Rockefeller University researchers Natascia Vedovato and David Gadsby demonstrate that, in addition to its role as a sodium and potassium ion transporter, the pump can simultaneously import protons into the cell. Their study not only provides evidence of “hybrid” function by the pump, it also raises important questions about whether the inflow of protons through sodium pumps might play a role in certain pathologies.
The sodium pump exports three sodium ions out of the cell and imports two potassium ions into the cell during each transport cycle. Vedovato and Gadsby show that, during this normal cycle, the pump develops a passageway that enables protons to cross the membrane. When the pump releases the first of the three sodium ions to the cell exterior, a newly emptied binding site becomes available for use by an external proton, allowing it to then make its way into the cytoplasm. The protons travel a distinct route, and proton inflow is not required for successful transport of sodium and potassium.
Import of protons is high when their extracellular concentration is high (pH is low) and membrane potential is negative. The authors therefore speculate that proton inflow might have important implications under conditions in which extracellular pH is lowered, such as in muscle during heavy exercise, in the heart during a heart attack, or in the brain during a stroke.
(Source: newswise.com)
Splice this: End-to-end annealing demonstrated in neuronal neurofilaments
While popularly publicized neuroscience research focuses on structural and functional connectomes, timing patterns of axonal spikes, neural plasticity, and other areas of inquiry, the intraneuronal environment also receives a great deal of investigative attention.
One example is the study of cytoskeletal polymers called neurofilaments –intermediate filaments of nerve cells that and a major component of the neuronal cytoskeleton believed to provide the axon with structural support. Neurofilaments are transported into axons where they accumulate during development, causing the axons to expand in girth. This is important because the cross-sectional area of an axon influences the rate of propagation of the nerve impulse. The space-filling properties of these polymers are maximized by spoke-like projection domains called side-arms that function to space the polymers apart. Once in the axons these polymers (which are barely 10 nm in diameter) can grow to reach remarkably long lengths – 100,000 nm (0.1 mm) or more – but how they attain such lengths and how their length is regulated is not known. Recently, scientists at The Ohio State University – who previously showed that neurofilaments and vimentin filaments expressed in nonneuronal cell lines can lengthen by joining ends in a process known as end-to-end annealing – demonstrated robust and efficient end-to-end annealing of neurofilaments in nerve cells. In additions, the researchers reported evidence for a neurofilament-severing mechanism.