Biological complexity: neuron pore complexity (Introduction)

by David Turell , Monday, October 05, 2015, 17:02 (3118 days ago) @ David Turell

Neuron pores controlling sodium and potassium ions are highly complex and allow neurons to rest after high speed firing:-http://medicalxpress.com/news/2015-10-ion-channel-reveals-neurons.html-"Within the brain, some neurons fire off hundreds of signals per second, and after ramping up for such a barrage, they need to relax and reset. A particular type of ion channel helps bring them down, ensuring these cells don't get overstimulated—a state that potentially can lead to severe epileptic seizures, among other problems. -***
"The signals that transmit information in the nervous system are generated by electrically charged atoms moving into and out of neurons. Typically, when a neuron fires, positively charged sodium rushes into the cell, generating a pulse of electrical activity that subsides as positively charged potassium floods out.-"In certain circumstances electrical impulses in the nervous system must be transmitted at a high frequency. But too high a frequency for too long can give rise to uncontrolled electrical activity, as seen in epilepsy, and can damage cells. For this reason mechanisms have evolved to put a protective break on the process. Slo2.2 underlies one such protective mechanism.-"The Slo2.2 ion channel does this by opening in response to the very sodium that enters the cell during an electrical impulse. When it opens, Slo2.2 allows potassium to flow out of the cell, thus restoring the cell's internal electrical state. It is not the only channel through which potassium travels; however, ions flow through Slo2.2 at ten times the rate of most other potassium channels.-***-"The researchers had obtained a full structure for Slo2.2 in its closed state. They uncovered a channel with four-fold symmetry. Inside the cell, where a potassium ion's path begins, two regulator domains (from each of four subunits) form a gating ring, which must open in order for potassium to pass. This ring, in turn, creates a massive funnel; when the channel is closed, the tip of this funnel is blocked.-"With this discovery, the researchers were able to better understand how Slo2.2 conducts ions so rapidly. When they mapped out the electrical charges across the channel's surface, they found the funnel has a strongly negative charge. It attracts positively charged potassium, creating a pool of ions waiting to exit once the gating ring opens.-"Once past the ring, an ion would traverse the cell membrane through a part of the protein called a selectivity filter that allows only potassium to pass.-"'Beyond giving us new insight on the basic configuration of this channel, this new structure also explains how Slo2.2 helps to quickly reduce the internal charge of a neuron and so rapidly return it to its resting state," Hite says. "Our next step is to determine Slo2.2's structure when it's open, which would help to explain how the arrival of sodium prompts the channel to open and allow potassium out.'"-The molecule involved is enormous. Look at the diagram of its structure. Ask the question. How did any unguided evolutionary process find this or invent it?