The gut feeling about caffeine

 Following from my previous caffeine post: What are the effects of caffeine on our bodies? I thought it's time to round off my investigation into the intriguing substance of caffeine.

Not the best way to find out the effects of caffeine on the body

Do you ever get that gut feeling when drinking coffee?-Coffee and the gastrointestinal system

There is strong evidence that coffee increases gastric acid secretion. Interestingly experiments have shown that it's the other constituents in coffee that contribute to this increase in gastric acid secretion.
This was shown by  measuring the dose response of caffeine, regular coffee and decaffeinated coffee for gastric acid secretion in normal subjects. Both regular coffee and decaffeinated coffee gave a similar response in gastric acid secretion which was higher than that of caffeine alone (on a cup equivalent basis) (Cohen and Booth, 1975).

The dose response? what??

Measuring the dose-response enables scientists to observe the change in an effect (in this case:gastric acid secretion) caused by varying the levels of dose of a substance (in this case: dosage of caffeine, regular coffee and decaffeinated) after a certain length of time.

Kidney function

The kidneys play an important role in filtering the blood. The kidneys remove waste products (such as urea) and extra water from the blood which form urine. Any drinker of caffeine beverages is well aware that caffeine tends to stimulate an increased flow of urine.

Anatomy of Kidney

Caffeine was traditionally used to increase urine output until more potent diuretics became available. The diuretic effects of caffeine appear to be due to an increased rate in blood flow to the kidneys and increased rate of blood filtration. These affects are due to antagonism of circulating adenosine (see previous post) having a regulatory role in the formation of urine  (Fredholm 1984).

So will my cup of coffee cause a fluid imbalance?
A dose of 300mg of caffeine (approximately 4-5 cups) can cause acute diuresis- this has been shown by several studies (Oswald and Schnermann., 2011). Caffeine will only cause a significant increases in the volume of urine excretion and a negative fluid imbalance in a large dose. A study in which caffeine was given (6mg/kg) for 11 days showed no effect in daily urine volume (Armstrong et.al 2005).

Time for a breather-Respiratory system

Caffeine is a respiratory stimulant (Braun 1996). However based on the average person's caffeine consumption has little effect on the respiratory system. Larger doses of caffeine has proven to be effective in the treatment of neonatal apnea-the cessation of breathing in newborns.

Upcoming posts

How about  I keep it a surprise this time?

References

Armstrong LE, Pumerantz AC, Roti MW, Judelson DA, Watson G, Dias JC, Sokmen B, Casa DJ, Maresh CM, Lieberman H, Kellogg M. 2005., Fluid, electrolyte, and renal indices of hydration during 11 days of controlled caffeine consumption. Int J Nutr Exerc Metab. 15

Braun S., 1996., Buzz: The Science and Lore of Alcohol and Caffeine., Cary., NC., USA., Oxford University Press
., 252-265. Cohen, S., and Booth, G. H. 1975., Gastric acid secretion and lower-esophageal-sphincter pressure in response to coffee and caffeine., New England Journal of Medicine., 293,897-899.

Fredholm, B. B., 1984.,Cardiovascular and renal actions of methylxanthines., New York:Alan R.Liss

Oswald H and Schnermann J., 2011., Methylxanthines and the Kidney., Handbook of experimental pharmacology., 200., 391-412.

Why can't the traffic on our roads be more like the traffic in cells?

Time to take a short break from caffeine. After all it's a special occasion with the announcement of the Nobel Prize 2013 winners! (It's about time I did a post about it)

I see science being a bit like a mystery to be solved: all the clues have to be gathered together to see the overall picture. However like scooby doo and his gang it is much easier solving the mystery together!

Likewise this years noble prize in medicine was awarded to three scientists: Randy Schekman, James Rothman and Thomas Südhof. Who uncovered how the cell organizes the transport of substances around the cell.

Cells have traffic?

So you're probably thinking how do cells have traffic?

Rules of the road: Cell style

Substances are transported around the cell in membrane bubbles called vesicles (these are a bit like taxis transporting passengers from A to B). Vesicles bud and pinch-off from specialised structures in cells called organelles. Vesicles travel along the cytoskeleton of the cell like taxis travel along roads. The cytoskeleton of the cell is a network of protein filaments and tubules in the cytoplasm of many cells. As well as its role in transport the cytoskeleton gives the cell shape.

Red showing cells actin cytoskeleton

Randy Schekman's contribution

He discovered a set of genes that were required for vesicle transport.
How did he do this?
He studied the genetic basis of how a cell organises its transport system by using yeast as a model. (Yeast  are often used experimentally as they can be grown quickly and have a eukaryotic cell structure-they have membrane bound organelles like human cells, we also share many genes with yeast cells). Sometimes the best way to discover how something works is to look at what happens when that system goes wrong. That's exactly what Schekman did. He studied yeast with defective transport systems, identified the cause of congestions and identified the mutated genes. So he had solved one aspect of cellular transport.

James Rothman's contribution

He revealed the proteins involved in the fusing of vesicles (the transporters of cellular cargo)  with their targets (their desired destination in the cell) enabling the vesicles to deliver their cargo. Through his experiments he showed that these proteins bind in specific combinations to ensure that cargo is delivered to a specific location.

Thomas Südhof

He was interested in how nerve cells communicate with each other in the brain. He showed how vesicular contents can be released as a result of a cell signal.

In nerve cells signals come in the form of neurotransmitters (chemicals such as acetylcholine and noradrenaline). Nerve signals pass from nerve cell to nerve cell at junctions called synapses. Südhof found how nerve cells release neurotransmitter into the synaptic cleft upon a signal.

When an action potential (a electrical signal) arrives at a nerve terminal, calcium ions enter the cell through a channel that is temporarily open due to the arrival of the action potential. The entry of calcium  causes vesicles containing neurotransmitters to be released into the synaptic cleft where the signal is communicated to the neighbouring nerve cell. Südhof discovered the calcium sensing proteins in the pre-synaptic nerve terminal which direct and dock vesicles containing neurotransmitter to the cell membrane where the neurotransmitter is released into the synapse (using the mechanisms discovered by Schekman and Rothman). See home-made diagram below (apologies I am no artist).

Synapse- Signalling between two nerve cells

Cells are incredible at transporting substances. It's interesting to see how the work of a few scientists have uncovered the mechanism of transport of substances. Hats off to them! I hope next time you're travelling you'll think about the trillions of cells in your body transporting substances to and fro.

Upcoming posts
More posts on caffeine are inevitable. Will hopefully be looking into reviewing scientific papers in the future-Watch this space.