We are finally descending into the heart of redox signaling country, we come to a place where there are many different pathways branching off in many different directions. And it looks like we are going to get wet. All of these redox signaling pathways are going directly into a huge ocean of salt water. We put on our scuba gear and tread in. There is no other way. All molecular activities in all forms of life on earth take place in salt water, it is the vital fluid of all life. All our cells and tissues are submersed in this ocean of fluids.
Under the salt water we find great currents of vital elements moving past in living rivers coursing throughout the extensive communities of living cells. Each cell is like a submerged house in this vast ocean, all of the cells are stacked in neighborhoods closely surrounded by these flowing rivers of currents; like houses along streets. These communities of cells are connected and fed by the currents that flow past them. Every living cell is alongside these moving rivers of life; each cell is connected by it.
Now imagine, if you can, this underwater community extends to fill all the oceans on earth, some 70 trillion houses; equivalent to every man, woman and child on earth today, each building 10,000 houses along these river currents. This represents the vast extent of the community of cells that exists inside just one living human being.
Of course, the rivers of life are mostly the networks of blood vessels–literally miles of them–feeding all the cells in our body. Our heart pumps this river of life though this vast network of blood vessels that connects and supplies our cells with all of the elements of life that they need. This river travels in only one direction, nothing much travels upstream. Along with oxygen, all of the fuel, building materials, chemical signals–everything needed to sustain life–travel along these rivers. The things that cannot be transported directly through the plasma fluid in the veins (for whatever reason) have little specialized “submarines” built for them to transport them down this river of life.
The cells have access to these currents of life through the receptor windows, chimneys, vents and doors. We can imagine the little molecular inhabitants of these cell houses floating in these fluids, swimming around inside their houses and between their houses under the water. The fluid that exists inside and around our cells in our body is somewhat similar to the seawater that is in our oceans. Blood plasma contains 0.9% salt, with a mixture of minerals; the ocean contains 1.9% salt, with similar types of minerals. We are now getting a better idea of what it really must be like to live in a community of cells.
With this picture in mind, it is easy to see that the fluid pathways that exist in, around and between our cells (individually and collectively) allow the molecules that are needed to sustain life (fuel, material, supplies or signals) to be available to all of our cells. It is also important to know that each living cell controls access to the “doors” and “windows”, and will not allow entry to just any molecule that happens to be floating by. In our cell communities, the doors and windows are called receptors and co-receptors and they selectively allow in only the fuels, materials supplies, and signals that are needed and used by the cells at any particular moment. Very few things can “seep through the cracks”. In this way, the cells have control over what is allowed to come in and what is allowed to go out. This selective behavior of the cells makes sense as we consider the complex logistics necessary for sharing resources among the trillions of cells in this thriving underwater community. Collectively, all of the fluid pathways constitute a vital one-way river of life that connects, surrounds, and passes through all of the cells, tissues, organs and systems of our body.
Another experience in this underwater world becomes very real to us. We cannot communicate with each other except by finding a way to send messages through the salt water that surrounds us. Since we have eyes, it may be easier for us to use lights or hand signals; but the molecular inhabitants of this world must have different, more interesting ways of communicating among themselves. In order to send a signal through water, the inhabitants have a limited number of options. If they have excess electrons or protons, they can use “email” and send electrical signals along the cables that connect the cells (neuronal material). If not, molecules can physically move with the currents between houses and travel like mail carriers to deliver the messages personally to the intended recipients (like hormones). Or, more interestingly, they can modify the molecules in the surrounding water (by reducing or oxidizing them) to and send ripple-like messaging to other nearby molecules through the surrounding salt-water medium.
Let us try to understand how this last form of communication works. How can life’s molecules modify the salt water molecules that surrounds them? We discover that as with all molecules, salt-water molecules can be reduced and oxidized (redox’d) through exchanges of electrons. Some biological molecules, like NADPH complexes, physically modify salt-water molecules (Na+, Cl–, H2O) and reorganize them into other molecules such as hydrogen peroxide (H2O2), super oxides (O2*-,HO2), hyperchlorites (OCl-, HOCl, NaOCl), captured gasses (O2, H2), ions (H+,OH–), and a variety of other molecules, ions and free radicals. These molecules are part of the class of redox signaling molecules that can send messages through the salt water. If you are curious to find a complete list, you can google Reactive Oxygen Species (ROS) and find all in this class of molecules. ROS are part of the fundamental class of redox signaling molecules found in all living organisms. There are other types of redox signaling molecules. If you add nitrogen (N2), which comprises 80% of the air we breathe, then nitric oxide (NO) can be formed, this is part of a class called Reactive Nitrogen Species (RNS). Then adding sulfur, very abundant in sea water, we also get Reactive Sulfur Species (RSS). ROS, RNS, and RSS comprise the class of redox signaling molecules that we are exploring. Each one of these redox signaling molecules can carry clear messages through the salt-water medium inside us. We simply could not live without them.
We have now become formally introduced to some of the ways that molecules can communicate among each other. Redox signaling may be by far the most interesting way of them all.
Welcome to redox signaling country!