Journal Club Discussion Post - Zach

My article looks at the belief that there is a gentic advantage for cystic fibrosis (cf) heterozygotes against forms of secretory diarrhea. CF is a hereditary autosomal recessive disease which affects the exocrine glands of the lungs, liver, pancreas, and intestines, and is in high frequency among Caucasians, 1 in 25. Specifically the article looks at the cystic fibrosis transmembrane conductance regulator (cftr) gene, which produces a chloride ion channel. In those with cf the channel is mutated therefore, chloride ions are not transported properly. In chloride ion channels that work properly water is released from the cell with the chloride ions. The agents used in the study, forskolin, cholera toxin, etc. all stimulate the release of chloride ions, which brings water with, and thus causes diarrhea. The hypothesis is that heterozygotes will not secrete as much chloride and therefore they are able to resist forms of secretory diarrhea.

The heterozygous mice used in the experiment were knockout mice, meaning they had only one copy of the cftr gene. The amount of chloride ions released by the gut epithelial was measured through short circuit current (SCC).

The agents forskolin and vasoactive intestinal polypeptide (VIP) were used to stimulate cAMP production triggering the release of Cl-, while the heat-stable enterotoxin (STa) and guanylin were used to stimulate cGMP for the release of Cl-.

Another way Cl- production was stimulated was through the use of Ca+ which when introduced to the cell produces cAMP or cGMP again releasing Cl-. This was done through the use of carbachol and lysylbradykinin.

None the these agents produced any significant difference between the two genotypes of mice.

One last thing the study did was to determine if frusemide inhibition levels were different. Frusemide was used to inhibit the transport of K+ and Cl-. The study suggests the two genotypes may release various amount of K+ which causes the SCC levels to be identical. If so, the inhibition effectiveness would be different between the two, however, no significant difference was found.

Overall the study did not find any significant evidence that heterozygotes enjoy a gentic advantage against secretory diarrhea.

I understand I probably didn't put everything in here that we would have talked about and I'm sorry but it was difficult to know where the discussion would go and how to put in what would be said. Anyways I will try and answer the questions as they come in an effort to make it seem like a discussion and clear up any confussion.


This paper went against a hypothesis of which I thought was well supported; binging heterozygous for the CF gene was advantageous in that it lessened the response to cholera, by lowering the number of working Cl channels and therefore lessening an infected person's diarrhea. After reading this article I get the impression that this hypothesis has not been well tested (this is coming from an ignorant position so very likely it is wrong). The experimenters knocked out one of the genes which coded for the Cl- ion channels, thus mimicking a heterozygous gene. But what Zach said is that this may not be truly representative. For having one gene transcribing for a malfunctioning ion channel and another for a properly functioning channel is not the the same as having one gene for the ion channel. This makes sense because I would assume resources are being used to make both the working and non working channels. I wonder having just one working gene would make more working channels available than having a gene making both the working/non-working channels. Again this is from Zach, it just makes my other questions seem insignificant, but I felt inclined to mention it. But I will state these questions anyways just because I think they are generally relevant and interesting to think about.

Let us assume for the purpose of this article that it is proved being heterozygous for the CF gene had no effect on the flow of Cl- across the cell wall. Now the following questions can be applied more generally as in any refutation of a believed hypothesis. And let us assume the evidence was very convincing. This evidence is strong enough that anyone would be moved to believe that it refuted the original hypothesis. (In the case of CF, those who carried one CF gene were less effected by cholera than those without.) So new evidence concludes this hypothesis to be highly unlikely. I have the following questions:

1) If one finds new evidence to disproved a long believed hypothesis, how does one go about getting the word out?

2) How does the scientific community feel about having a long accepted hypothesis refuted?

3) Does it take a ling time for this new evidence to make it into academia?

4) Must the experimental technique be repeated many times by others in the field in which it is most important (Chemistry, biochemistry, microbiology, physiology, ect.)

5) How great would it feel to be the one who does the disproving. Y'all could guess that I would love it. "You're Wrong!"

6) Don't you love the idea of the possibility of going into the science field and f*ckin sh*t up?

7) Why are people having sex with monkeys? It can't be so good that it is worth spreading AIDs to the human race. Or is it? (this is just to see if anyone is even reading this crap) Collin, you are one sick and twisted individual… but I guess that's what keeps the class spicy. -Chad

That's all I have for now, but great paper and great topic. I can't wait to find more out about CF and cholera


Colin, your #7 is not funny. Unless you are the one having sex with monkeys — you are assuming too much about a devasting disease. It is too easy to point fingers. I know it was just a joke but come on, really?

I was just wondering whether or not there is a genetic preference with the rest of the organs. Does this pertain to just cholera and E.coli. What about other things that cause diarreha? Is studying the murine proof enough or have they seen this in humans by looking at "heterozygous" parents of CF sons/daughters? Is there a link like malaria and sickle cell?

What I don't understand is that the researchers are stimulating the Chloride ions to cross the membrane in both cells and trying to see if there is a difference. What I am having trouble with is that only those transmembrane proteins associated with the cftr are affected. Are there not proteins that can transport chloride besides these proteins? So I would think that there would not be a change, but I do think that the chloride being transported by the cftr genes would be less. Since those are less the other proteins are transporting more chloride across to make up for the cf. Just a thought.

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