What is "alive"?

[lucaspa]

This is from a paper titled "Insulin signalling through ultradian oscillations":

 

"Periodic oscillations appear to be a characteristic of insulin secretion at various different levels. Very rapid pulsations are seen in the isolated b-cell and islet, while rapid (10- to 15-min) pulsations are seen both in the intact organism and in the isolated pancreas."

 

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WG5-4G23KWF-4&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=d7f83ab25463c4e1ed9000ae3f1ae252

 

Stevo, very good for finding a reference on the subject. However, you need to read the scientific literature a bit more carefully. In this case, what they are looking at is not "pulsation" of the cell, but pulses in the secretion of insulin. It's subtle, and I'm not surprised you missed it, but the key sentence in the Abstract is here: "Very rapid pulsations are seen in the isolated β-cell and islet, while rapid (10- to 15-min) pulsations are seen both in the intact organism and in the isolated pancreas." Your entire body does not "pulse", does it? Nor does an isolated pancrease "pulse". Instead, what is detected is "pulses" of insulin release. Insulin is not released in a steady stream, but instead in packets as the secretory vacuoles containing the insulin fuse with the cell membrane and then release the contents of the vacuole. So this isn't what you think it is.

 

But good work on researching the literature.

 

This is from a paper titled "Osteocytes as multifunctional cells":

 

Osteocytes can move

 

Again, I compliment you on your search of the scientific lineage. As a "bone person" I find this very interesting. Again, you need a bit more experience and subtlety in the scientific lineage. First, what is the author Bonewald arguing against? "Bone is often thought of as being a passive, inactive tissue like a skeleton hanging in the anatomy lab. ...However, quite to the contrary, bone undergoes considerable turnover as compared to other organs in the body."

 

This is a bit of a strawman, since no one in the bone field has thought of bone as an "inactive" tissue for at least 50 years.

 

Now we go to this: "Evidence is accumulating that osteocytes are more active than previously known."

 

That also is a bit of a strawman. We've known for 10 years that osteocytes participate in 1) calcium uptake and 2) transduction of mechanical loading. I talked about the first when I said "When stimulated by parathyroid hormone, they respond by taking calcium out of the bone and moving it from one osteocyte to another until it can be dumped in the blood."

 

Now comes the part that you like: " Dallas and colleagues will show at this meeting that osteocyte cell body movement occurs within lacunae and that extension and retraction of dendrites can occur within canaliculi."

 

All fine and good. Notice the part I bolded. BUT, when I look at the article referenced (20) to back this up "Calvaria from these mice were used to image living osteocytes within their lacunae20" we find that it is "in press". When I go to PubMed to try to find the article using the authors as my search term, I find that it doesn't exist! This is common. Only about 1/2 of the presentations at meetings ever find their way into the peer-reviewed literature. That's the purpose of meetings: to do an initial "cut" of good research from bad research. The person who wrote the article you quoted is also one of the authors on the paper "in press" that is necessary for your argument. So of course Bonewald thinks the presentation is good data! But apparently it wasn't because the "in press" article wasn't really in press at all. It had probably been submitted and the authors thought it would be accepted, but it wasn't.

 

It would appear that the “fact” of the immobility of the pancreas cell and the osteocyte is not etched in stone, and may in fact be altogether wrong.

 

Yes, as an admitted "layman, with almost no formal scientific education", it would appear to you that what I said was wrong. However, I never considered it comical. Nor do I now. There are subtleties to the scientific literature that someone without experience will miss. I hope I have clarified how the data is not what it appeared to you. I'm afraid my falsifications of "movement" remain falsifications. Altho, it may be that we will find -- with better data than Bonewald had -- that osteocytes do extend and contract their dendrites. However, I doubt it. Transmitting the signals of mechanical force thru the osteocyte network requires that the dendrites remain in contact so that chemical signals can move from one osteocyte to another. I suspect that the "extension and retraction of dendrites can occur within canaliculi" was an artifact as the osteocytes died during the experiment (which was probably one reason why the paper did not make it thru peer-review).

 

I just think that pulsation is fundamental to living organisms.

 

Now you have changed the argument. You started out saying "movement" was fundamental to living organisms. Now you are saying "pulsation", which means staying in one place but moving cell shape.

 

Your next "assignment" is to look at the literature on algae. Free floating single celled plants. See if you can find any data that they "pulsate".

[stevo247]

I just think that pulsation is fundamental to living organisms.

 

Now you have changed the argument. You started out saying "movement" was fundamental to living organisms. Now you are saying "pulsation", which means staying in one place but moving cell shape.

 

I thought that I had clarified the particular “manner of movement” of living organisms in a previous post:

 

Perhaps the nature of the movement we are talking about is different than say a hammer hitting a nail (i.e. a mechanical reaction).

 

If this is so, then you need to make a new criteria for being alive than simple "movement", don't you? Which is what we have been saying all along.

 

It appears to me, that living things have a very particular “way of moving”. If I was to reduce that manner of movement into its simplest form, it would have to be expansion and contraction, or pulsation. I don’t think non-living things pulsate.

 

Maybe I'm not being clear. I think that living organisms function in a pulsatory manner. That pulsation is inherent in all living processes, and that expansion and contraction are fundamental characteristics of pulsation. As far as I can tell, all living things seem to be rooted in a common functioning principle of pulsation.

 

Clearly, the heart pulsates. Respiration is pulsatory (expansion and contraction of the lungs). Digestion (peristalsis) is pulsatory. Ejaculation is pulsatory. The bladder expands and contracts, pulsatory. The amoeba moves in a pulsatory manner. The “beating” of a birds wings are pulsatory. A snake moves in a pulsatory manner. Pancreas cells secrete in a pulsatory manner. Inchworms move in a pulsatory manner (expand/contract). Fish swim in a pulsatory manner. Personally, I would nominate the jelly fish as the poster-child of pulsation in nature. Etc. etc. etc. Whenever I investigate something of a biological nature, I see pulsation as a chief feature of it's functioning. From the multicellular to the unicellular. “As above, so below”.

 

But when I look at a rock, I wouldn't characterize it as functioning in a pulsatory manner. The same with my desk, or my shoe. “Inanimate” objects. No pulsation function. Not living.

 

Your next "assignment" is to look at the literature on algae. Free floating single celled plants. See if you can find any data that they "pulsate".

 

 

You were wise to point me in the direction of algae. They are a diverse group and many have a cell wall which is more or less rigid. Many dinoflagellates are characterized as “armored”.

 

“Many are covered by cellulose plates.

The cell is surrounding by a series of membranes called the amphiesma. In "armored" species cellulose deposited between the membranes forms rigid plates called thecae. "Naked" cells lack thecae.”

 

http://www.assurecontrols.com/info-dinoflagellates.htm

 

To me, this is comparable to a turtle shell. The shell does not demonstrate the pulsation function, but the turtle in the shell does. Pokes his arms, legs, and head out (expand). Pulls them back in (contract). Not to mention all the pulsatory metabolic processes going on in the turtle itself.

 

I would say that the dinoflagellate demonstrates the pulsation function in all realms of it's functioning, except for the armored, rigid, membranous, shell.

 

Here is an algae that clearly demonstrates the pulsation function:

"The euglenoids can glide and swim using their flagella, or can ooze along a substrate with an undulating, shape-changing, contraction motion called metaboly."

 

http://silicasecchidisk.conncoll.edu/LucidKeys/Carolina_Key/html/Euglena_Main.html

[tyrant09]

What are your opinions in the life of viruses? Viruses indeed reproduce and are parasitic in nature, yet they do not execute metabolic functions.