11.2 Movement

Developments in scientific research follow improvements in apparatus—fluorescent calcium ions have been used to study the cyclic interactions in muscle contraction

 In a review article of the use of Calcium imaging in physiology studies, Russell notes that calcium ions are:

“…an ubiquitous intracellular messenger that regulates multiple cellular functions such as secretion, contraction, cellular excitability and gene expression in all organ systems.” (Russell, 1605)

We have encountered them in detail in looking at synapses and muscle contraction in animals and also their role in the formation of the cell wall in plants.  Clearly calcium is an important element whose roles range wider than just making healthy bones and teeth!

Advances in technology enable us to collect data that is otherwise outside the the abilities of human perception; this provides the evidence to develop theories.  In 1962 it was reported that scientists had extracted a Ca2+-sensitive bioluminescent protein from the jellyfish, Aequoria victoria.  and gave it the name “aequorin”. Aequorin emits light when it reacts with calcium and this can be detected experimentally by illumination with different types of radiation. In many cases, a light microscope can be used to view it and it can be photographed or filmed as well.

1024px-Aequorea4
Aquorea victoria (Sierra Blakely)

In topic 11.2 we learn about the role of calcium from the sarcoplasmic reticulum binding to troponin and thus triggering the contractile cycle of actin and myosin.  A recent study (Desai et al.) used calcium fluorescence to tag individual molecules of myosin in order to image how single filaments of myosin interact with ATP and Calcium to activate the actin.  The team were able to determine that two myosin heads are needed to activate the actin filament and that 11 Myosins bind as part of a regulatory unit.

As technology advances, our understanding of biological processes grows deeper and more complex. This in turn either provides additional evidence in support of existing theories or may suggest alternative explanations.  And so science moves on….

Sources:

Allott, Andrew, and David Mindorff. Biology: Course Companion. Oxford, Oxford University Press, 2014.

Blakely, Sierra. “ Aequorea Victoria .” Aequorea Victoria , Wikipedia, 17 Feb. 2017, en.wikipedia.org/wiki/Aequorea_victoria. Accessed 20 Apr. 2017.

Desai, Rama, Michael A. Geeves, and Neil M. Kad. “Using Fluorescent Myosin to Directly Visualize Cooperative Activation of Thin Filaments.” The Journal of Biological Chemistry 290.4 (2015): 1915–1925. PMC. Web. 20 Apr. 2017.

Russell, James T. “Imaging Calcium Signals in Vivo: a Powerful Tool in Physiology and Pharmacology.” British Journal of Pharmacology, vol. 163, no. 8, 2011, pp. 1605–1625., doi:10.1111/j.1476-5381.2010.00988.x.

Zimmer, Marc. “Green Fluorescent Protein.” Green Fluorescent Protein – The GFP Site, Connecticut College, 18 Aug. 2015, http://www.conncoll.edu/ccacad/zimmer/GFP-ww/GFP-1.htm. Accessed 20 Apr. 2017.

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11.3 The Kidney and Osmoregulation

Curiosity about particular phenomena—investigations were carried out to determine how desert animals prevent water loss in their wastes.

Water, water, every where,
And all the boards did shrink;
Water, water, every where,
Nor any drop to drink.
The Rime of the Ancient Mariner

As a zoology major at university, I spent many hours pouring over Knut Schmidt-Nielsen’s classic text, Animal Physiology. He was  widely regarded as the father of comparative physiology and made groundbreaking contributions to the discipline of  Ecophysiology, the study of how animal physiology is adapted to the environment. A group of animals that came in for particular notice in many of his studies were the desert rats (Dipodomys sp.).

dipomerr
Merriam’s Kangaroo Rat (Dipodomys merriami) (Dr. Lloyd Glenn Ingles, 1999)

These rats eat only dry food, principally seeds, yet almost never drink water, even if it is available. Their habitat, the deserts of SW North America, see little rainfall and baking temperatures. How is this possible?

Firstly, a primer on water balance (adapted from Schmidt-Nielsen, 1962). Animals gain water through either drinking free water, water in their food and the water produced from the oxidation of glucose in respiration (metabolic water). Water is lost from the body by evaporation from the skin and lungs, in urine and in feces.  In order to survive without drinking water and on a dry-food diet, these animals must therefore minimise their water loss. As this topic is linked to 11.3 (Osmoregulation) we will focus on their kidney adaptations.

We learn when studying topic 11.3 that the Loop of Henle is crucial in allowing the development of a urine that is hyperosmotic to the blood plasma. Desert rats have a proportionally very long Loop of Henle and a thicker medulla, which allows for the establishment of even more concentrated urine.  Additionally, as a small animal, their high metabolic rates mean they have more densely packed mitochondria and transport pumps throughout the nephron, allowing the maintenance of a concentration gradient.

The result is that various species of desert rats can excrete a urine that is up to 16 times the concentration of their blood plasma and over four times more concentrated than seawater!

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adapted from Willmer et al. 2011

With a greater amount of solute in the urine, proportionally less water is needed to excrete it. These rodents also take it a step further by producing very dry, pellet-like feces.  They also ingest their feces to reabsorb what little water is in them.  They are therefore able to survive only by using metabolic water and the water in their food – a useful adaptation for the desert.

But the curiosity doesn’t end there!  Schmidt-Nielsen wanted to know if they could survive on drinking seawater.  Seawater has a concentration of between 1000-1200 mOsm/L. If a human drank 1 litre of seawater, they would need 2 litres of urine to flush out the excess sodium chloride, thus leading to dehydration very quickly.  But given the ability of the desert rat kidney’s to concentrate the urine, he reasoned that they should be able to do it.

Firstly, to induce thirst, he fed the rats on a diet of soybeans. These are high in protein and produce a lot of urea that needs to be removed.  Normally, the rats don’t drink water so they need to be induced to do this; the high protein diet accomplishes this. He then provided different groups of rats seawater, freshwater and no water. The results are displayed below:

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The results of providing sea water to desert rats (Schmidt-Nielsen 1962).

Amazingly, the rats provided with sea water showed no change in body weight after 2 weeks, almost exactly the same as those provided with fresh water.  Proof of the tremendous concentrating power of their kidneys, and more specifically, their loops of Henle.

And remember, should you ever be stuck on a becalmed ship or wrecked on a desert island, don’t drink the water!

Sources

Coleridge, Samuel Taylor. “The Rime of the Ancient Mariner .” Poetry Foundation, Poetry Foundation, http://www.poetryfoundation.org/poems-and-poets/poems/detail/43997.

Ingles, Dr. Lloyd Glenn. “Merriam’s Kangaroo Rat (Dipodomys merriami)”  University of Texas, El Paso. museum2.utep.edu/chih/theland/animals/mammals/dipomerr.htm, 1999. Web. 9 Feb. 2017.

Schmidt-Nielsen, Knut. “Comparative Physiology of Desert Mammals.” Agricultural Experimental Station, vol. 21, Dec. 1962, animalsciences.missouri.edu/research/bec/Brody%20Memorial%20Lectures%201/Lecture%202%20Knut%20Schmidt-Nielsen.pdf.

Willmer, Pat, et al. Environmental Physiology of Animals. 2nd ed., Malden, Mass., Blackwell Publ., 2011.

11.4 Reproduction (HL)

Assessing risks and benefits associated with scientific research—the risks to human male fertility were not adequately assessed before steroids related to progesterone and estrogen were released into the environment as a result of the use of the female contraceptive pill.

There are a lot of myths surrounding the environmental effects of the contraceptive pill, despite the fact that it is one of the most widely-taken and best studied drugs in use. According to the ARHP, more than 13 million American women use the pill and there is over 50 years of data on its safety and effectiveness (Moore et al.).

Concerns have been raised that the additional estrogen, largely a synthetic estrogen called Ethinyl Estradiol, being released into the environment through usage of the pill has resulted in elevated rates of these hormones in drinking water.  As steroid hormones, these are known as Endocrine Disruptive Chemicals (EDCs) – chemicals that could alter the hormonal balance and control of organism’ physiology (Moore et. al.) Clearly then, there are legitimate concerns for the health impacts of any chemical that can disrupt an animal (or person’s) endocrine system.  The increase in male infertility as well as the recorded feminisation of some species of fish over this time period has amplified this issue. But is the contraceptive pill a significant part of this problem?

A comprehensive review (Wise et al.) examined this statement and found that the contraceptive pill is a negligible cause of any synthetic estrogens in waterways. It does highlight the role of agriculture and industry as sources of EDCs; for example, it points out that the amount of synthetic estrogen given to livestock in the US is five times greater than that consumed by all the women on the pill (Wise et. al.)

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Sources of endocrine-disrupting compounds in the water supply (Moore et al.)

Returning to the statement in the Nature of Science, there remains the issue of whether the risks were properly considered before the widespread use of these drugs and thus whether a full ethical review was conducted.  However, the link between estrogen compounds in the environment and the pill seem tenuous at best and it is other sources of steroid-based hormones that need to be addressed.

Sources:

Moore, K. et al. Birth Control Hormones In Water: Separating Myth From Fact. arhp.org. 2011. Web. Mar 30, 2016.

Wise A, O’Brien K, Woodruff T. Critical review: are oral contraceptives a significant contributor to the estrogenicity of drinking water?. Environ Sci Tech. 2011;1:51–60

11.1 Antibody production and vaccination

Consider ethical implications of research—Jenner tested his vaccine for smallpox on a child.

The story of Edward Jenner is a fascinating one and he played a key early role in the development of vaccines. The PBS Series “Rx for Survival” has a nice little dramatisation on his vaccine research in Episode 1: Disease Warriors (9m 13s – 12m 01s), though the whole episode is worth watching.

Jenner had noticed that milk-maids contracted cow pox, a non-fatal disease from cows, in the course of their work.  While this might make them ill for a time, they rarely ever caught the much more dangerous relative of cow pox, small pox. To test his theory, he inoculated a farm boy with pus from a milk-maid’s cow-pox pustules; the boy was unwell for a few days but made a full recovery. Jenner then exposed him to live small pox virus and he survived.

The ethical issues seem clear, but on reflection may not be so cut-and-dried.  Under modern medical standards, it is considered unethical to expose patients to live, virulent strains of a pathogen in order to test the efficacy of a vaccine. Such experiments would also not be done on children as young as eight. It is also likely that Jenner never received informed consent for the experiment as well.

However, there is a good case to be made that Jenner was merely following the ethical standards of the day, and that in fact, inoculation of this sort was relatively common in rural England (Abc). Given the very real danger of contracting the fatal small pox, it might be argued that the possibility of protection from the disease was sufficient motivation.  We can also link to TOK here and think about the challenges of applying modern ethical standards to past events, particularly where the context is so very different to today.  This link is a very nice ethical discussion of this, including a hypothetical hearing before an ethics review board (Davies).

It was not without controversy at the time, however, with the anti-vaccination movement already forming its arguments.  The famous cartoon below shows their misplaced fears:

The_cow_pock
The Cow Pock – 1802 (Wilson and Marcuse)

Sources

Abc. Ockham’s Razor: Defending Edward Jenner, 2015. Web. 15 Dec. 2015.

Bioethicscourse.info,. “Jenner On Trial: Introduction”. N. p., 2015. Web. 15 Dec. 2015.

Davies, H. “Ethical Reflections On Edward Jenner’s Experimental Treatment”. Journal of Medical Ethics 33.3 (2007): 174-176. Web. 15 Dec. 2015.

Wilson, Christopher B., and Edgar K. Marcuse. “Vaccine Safety–Vaccine Benefits:Science And The Public’s Perception”. Nat Rev Immunol. 1.2 (2001): 160-165. Web. 15 Dec. 2015.