Puzzling over caffeine and adenosine-it's time to talk about receptors (please don't be antagonistic!)

Heading back to university for the start of the academic year it'll be inevitable that my coffee consumption will increase exponentially. So I'm back again and thinking about what happens in my body when I consume my daily caffeine fix.

After looking at caffeine metabolism and whether caffeine is addictive and causes insomnia in my previous posts. I thought it was time to start looking at HOW caffeine changes our body's functioning.

So time to start fitting the pieces together of the physiological effects of caffeine. This starts with receptors.

What are receptors?

Receptors are proteins which can be found on cell membranes. They bind to specific chemicals (these could be hormones, drugs, neurotransmitters etc). The binding of these chemicals can cause a change to occur in the cell.

It is natural when looking at the biological effect of caffeine in the body to start looking at what happens when caffeine binds to a receptor.

The caffeine-adenosine relationship

Everybody has two friends which are uncannily similar to each other. Caffeine and adenosine are those uncannily similar friends-they have a similar molecular structure.

Spot the difference for the chemists!

These similarities in structure mean that caffeine can bind to adenosine receptors and block their function. Adenosine on binding to its receptor generally inhibits physiological activity (it makes us feel more tired). Due to adenosine and its half brother caffeine having a similar molecular structure caffeine blocks adenosine receptors (mainly  A1 and A2 types of adenosine receptors) preventing their activation resulting in caffeine having a stimulant effect. Hence caffeine is an antagonist (It interferes with the binding and physiological affect of adenosine).

Still puzzled?

So if that’s perhaps gone over your head a little......

 Imagine you are putting together pieces of a puzzle. You are looking for a piece of the puzzle that joins to the piece you have in your hand (the adenosine receptor). You can see two similar looking pieces on the floor (an adenosine and caffeine molecule) that look like they'll both join onto the piece you are holding. You try piece A (the caffeine molecule) and find that it pretty much fits onto the piece you are holding (the receptor) but the fit is not perfect. Despite this you decide to continue putting the puzzle together. However you find that you cannot fit the rest of the puzzle together and complete it (receptor has not been activated so the physiological effect is inhibited-completing the puzzle) as the two pieces you first joined together are not the correct pieces to join to complete the puzzle (the physiological effect is inhibited).

You go back to the original piece you had in your hand (receptor) and this time you join piece B (the adenosine molecule) onto it and find that these two pieces fit perfectly together. This time you find you are easily able to complete the puzzle (the receptor is activated resulting in the full physiological effect-the puzzle is completed) as all the other pieces fit around the two you first joined together (the receptor and adenosine molecule).

Let’s put the puzzle together....

The binding of caffeine to adenosine receptors prevents adenosine from binding to the receptor causing a change in the cell's behaviour. Caffeine inhibits the effect of adenosine. This is how caffeine can make us feel more awake. As adenosine decreases neurotransmitter release, dilates blood vessel and inhibits lipolysis (break down of fats)-these effects make us feel more tired. Caffeine preventing this in turn makes us feel more awake.

Upcoming posts....

Caffeine and its effect on the physiological processes in our body- how this stimulant takes its effect on the nervous, gastrointestinal, respiratory systems and renal function.