Biological complexity: controlling cellular potassium (Introduction)

by David Turell , Friday, December 23, 2016, 21:33 (2892 days ago) @ David Turell

Another complex mechanism controlling the cellular potassium levels has yielded to research:

http://phys.org/news/2016-12-molecular-reveals-cells-spew-potassium.html

"New research from Roderick MacKinnon's Laboratory of Molecular Neurobiology and Biophysics at The Rockefeller University has determined, for the first time, the complete structure of an ion channel that plays an important role in cellular electrical signaling by sending potassium ions out of the cell at an extremely rapid rate.

"By revealing new insights into how the molecule works, this research leads to a deeper understanding of the link between the membrane and processes inside the cell, including calcium regulation of electrical signals, which is central to muscle contraction and neural activity.

***

"Potassium channels both regulate the occurrence of electrical impulses and terminate the impulses once they are generated. One such potassium channel, known as the BK or "big potassium" channel, conducts ions up to a level 20 times that of other potassium channels. To do so, BK responds to two separate triggers—electrical activity on the cell membrane and levels of calcium—that it ties together

***

"The pore within BK is much wider than those of other potassium channels. In fact, it forms a wide funnel that opens up to the interior of the cell," Tao says. "And the funnel's surface bears a negative charge, which attracts positively charged potassium ions from within the cell toward the pore."

"In order for potassium to flow through BK, the channel's pore must open, and it does so in response to two triggers: calcium, another ion important to cellular signaling; and a change in voltage across the cellular membrane, which occurs when a cell generates an electrical impulse."

After binding to calcium ions, the channel compresses itself, changing shape in such a way that its pieces are pulled outward and the pore widens.

While the researchers could not directly observe how the channel responds to a change in voltage, the structure did provide clues to explain this opening mechanism. Sensitivity to both calcium and voltage most likely allows the channel to fine-tune its responses, the researchers say.

Comment: Rapid movement of potassium is essential to the speed impulses travel along nerves and the speed of response of contracting muscles. Remember this is just pore shape and control, and dos not address the other chemical mechanisms that determine when to flush the potassium. this is all highly complex, and like all other integrated functions must have developed by saltation. Bit-by-bit or trial and error just doesn't lend itself to developing this sort of complexity. Look at the moving diagram of the pore, and marvel at the size of the molecules involved.