Tune In to Channel Kir2.1
A molecular machine with exquisite sensitivity
has been shown in atomic detail for the first time.
The central nervous system of man and animals depends on electricity:
the ability to maintain a voltage between the inside and outside of a cell membrane.
How can an electrical voltage be achieved by a cell? Osmosis, a law of nature, tends to move substances at high concentration toward areas of low concentration until equilibrium is reached. Active transport, by contrast, is a key part of life. It requires pushing materials against the concentration gradient (see video). The cell achieves active transport by use of molecular machines: membrane channels that can selectively filter needed materials (atoms, molecules or ions) and move them against the gradient where they would otherwise “want” to go. These include aquaporins that filter water, vesicles that can package and move molecular cargoes, and the amazing “voltage-gated” channels that can move ions. One of those, Kir2.1, has been elucidated in exquisite detail by scientists at the Sorbonne University in Paris.
New methods of super-resolution microscopy are opening windows into cellular machines like never before. One of the leading methods is called cryo-electron microscopy. This involves flash-freezing molecular machines so that electron microscopes can image them at an instant of time, like frames of a movie. Enough frames taken at different times allow scientists to construct a “movie” of the machine’s action. With this method, biochemists can image molecular machines at the nano scale, almost imaging the position of individual atoms themselves.
Source: Fernandes et al., Cryo–electron microscopy unveils unique structural features of the human Kir2.1 channel. Science Advances 23 Sep 2022, Vol 8, Issue 38, DOI: 10.1126/sciadv.abq8489.
The paper is open access, so take a moment to browse through the figures and see how this marvelous machine looks. As you look at it, realize that your brain and heart are actively pumping potassium ions through these filters at rates like ten million per second (Cell Biology by the Numbers).
Side and top views of the Kir2.1 voltage-dependent rectifier channel, from the paper.
How it Works
Kir2.1 is a “rectifier” – a term that will be familiar to electronics enthusiasts. Rectifiers allow current to flow one way. In electronics, rectifiers can turn alternating current (AC) to direct current (DC). Cell rectifiers do essentially the same thing: they rectify charges from one side of a divide to the other, making them go one way.
For the cell membrane to rectify charges (i.e., create a voltage), positively-charged ions like potassium (K+) must be pumped through the channel to the inner membrane. A series of four “gates” ensure the one-way passage of these tiny ions. First is a “selectivity filter” that collects the ions. These pass rapidly down constrictions that open and close just enough to let the potassium ions through while blocking other molecules and ions.
The inward-rectification mechanism results from a block on the cytoplasmic side of the channels by endogenous polyamines and Mg2+ that plug the channel pore at depolarized potentials, resulting in decreased outward currents. The blockers are then removed from the pore when the K+ ions flow into the cell at hyperpolarized potentials. This voltage-dependent block results in efficient conduction of current only in the inward direction.
The channel is thus self-regulating, sensing the voltage and opening or blocking its constrictions according to need. If that weren’t amazing enough for an electronics device at the nano scale, this channel also receives signals that make it respond to changing environments. The authors list four examples. They also say that Kir channels are coded by 16 genes, which implies that the protein parts must be delivered from the nucleus to ribosomes and then delivered to sites on the membrane where they will be needed. The channels must be inserted into the membrane in the right orientation, implying additional quality control mechanisms.
If any of these precision channels are messed up by mutations, bad things happen. “Genetically inherited defects in Kir2.1 channels are responsible for several rare human diseases, including Andersen’s syndrome,” the authors state. Good thing it is rare; the defect causes “abnormal heart rhythms, physical characteristics including low-set ears and a small lower jaw, and intermittent periods of muscle weakness known as hypokalaemic periodic paralysis.”
For an interesting look at the element potassium (K), where it is found on earth, and how it gets incorporated into living things, see this video about potash on the popular YouTube channel Veritasium. Read also Howard Glicksman’s article about potassium in the body on Evolution News.
The paper nowhere mentions how this beautiful little rectifier might have originated by chance. As the video link in the top paragraph shows, no primitive “protocell” could ever work without a host of channels in their membranes that can selectively block unwanted materials and allow in necessary materials. When you examine the detail of the parts of any one of these channels, the implication of intelligent design should be overpowering.
Most of us live moment by moment unaware of all the designed machines inside of us that keep us ticking. We should learn more about some of them just to increase our awe of life and stand humbly before the Creator who designed these wonders.
Unfortunately, the majority in academia accept the chance explanation because of their prior commitment to materialism. Assuming materialism, they effectively shut their eyes and minds to the possibility that these devices were intelligently designed. That ignorance is reinforced by the majority of their peers, who have been led throughout school to reject design as a possibility.
One can only hope that individual scientists, looking at these devices with their electron microscopes, investigating all the fine details, will stop and think: “Wait a minute; that looks designed. How could something like that ever come about by chance?”