Cells, both in your body and in other living organisms of all types, need a way to move useful substances into themselves and pump wastes outside. The wall of the cell, the boundary across which this has to be done, is called the cell membrane, or plasma membrane. It is a complicated structure that is composed largely of special lipids (that is, substances that resemble fats or oils) but that also includes many proteins and other substances or mechanisms that help the cell do its job, whatever that might be. Proteins in the cell membrane act like little machines, interacting with other molecules and moving them around or communicating information through changes in their shape. In many cases the process of moving materials through the cell membrane has to be extremely carefully controlled, because substances that are needed in small quantities may be poisonous to the cell in large quantities. For this reason, cells create and install in their own membranes structures called channel proteins that enable very specific substances to move into or out of the cell. A channel protein can act as just a tunnel for all molecules below a certain size, or specifically select an exact molecule and actively force it through the membrane in only one direction, or anything inbetween. The cell can control its membrane traffic my making more channel proteins of a specific type, or removing them from the membrane to be recycled for parts. Think of them like bouncers at a night club with different personalities. One bouncer may stand at the front door and allow in any female human over the age of 18, while another loiters near the side door and forcibly ejects loud, intoxicated men who appear to be picking a fight. The club owner can select the mix of people inside by having a lot of different bouncers available and choosing how long and when to post each bouncer at the appropriate door. Of course, cells do not have intelligence and will, so the "decision" is made through signal processing in the cell's nucleus in which internal or environmental cues cause different parts of the cell's DNA to be translated or "turned on," resulting in different proteins, including channel proteins, being made. There is one more small complication here, in that many important substances, like water and oxygen, cross the cell membrane without passing through a channel protein, in a process called passive diffusion. The cell can sometimes influence the movement of these substances, however. As an example, water "follows" sodium ions when they are moved through the cell membrane. If the cell wants to absorb more water, it can therefore turn on a pump that moves sodium inside. This is one of the ways your body controlls its hydration state, and why salt is so bad for many people with high blood pressure: lots of sodium in the body means water stays inside (instead of leaving through kidney cells and then the bladder) which means there is more blood volume and blood pressure is higher. Folks with high blood pressure may have mixed-up signals controlling their sodium channel proteins, and don't pump enough sodium out into the urine to get rid of it. It's your kidney cells, not your heart, that control long-term blood pressure! There aren't any channel proteins that move other proteins. They are moved in and out of the cell by very different processes called endocytosis and exocytosis. So, if you've come across the term "protein channel" it could be because the two words got mixed around when someone wrote them down, or because there was confusion about the method for moving proteins. One sort-of exception would be the channel proteins in the wall of your intestine that bring broken-down proteins into your body. Those don't move full proteins, though, but rather amino acids, the building blocks that make up proteins. The full protein you eat as meat, beans, nuts, etc is broken down by chemicals from your pancreas into individual amino acids that the intestine's channel proteins can handle.