In article <CxIqEI.93z at nntpa.cb.att.com>, norm at chico.uucp (Norman E.
Andrews [ MT 2C-402 9089575786 NC6241000 ]) wrote:
> I don't think you mentioned in vivo tests, but I'll bring that subject up.
> One can still interpret the aging differences between in vivo and
> in vitro as an artifact of inadequate culture technique, if the nutrition
> delivery and waste/immune system disposal systems??? of in vivo differ from
> and are probably better than what scientists are now able to provide in vitro.
> So what I am suggesting is that there may indeed be a genetically related
> Hayflick limit that occurs with in vitro testing, but that such a limit
> may not exist in vivo, or if it does, perhaps not to an extent that explains
> the sensescence of man. I am ignorant of whatever in vivo testing may have
> been done to explore this.
I don't know if this helps, but there also seems to be a relationship
between the telomeric length of cells and its age. With each division,
the telomeres on each chromosome shorten. However, in cancer cells this
does not happen. Their telomores are kept at a constant length. It is my
understanding that normal cells do have telomerases that keep up their
telomores, but I guess they just don't do it at as an efficient rate as
the cancerous cells.
> I fail to see your conclusion in [1]. One simple and perhaps wrong
> explanation will serve to illustrate: Suppose the metabolism of the
> different cell types proceeds at different rates, but that they all
> require something that is inadequately provided by the culture
> technique, perhaps nutrition or waste disposal. There would be
> a genetic link, expressed thropugh different rates of metabolism, but
> the inadequate culture technique could be the cause of existence
> of the (different) Hayflick limits. The magnitude of the differences
> would be genetically related, but the _existence_ of the limit would be
> because of the culture technique.
I think the difference in metabolism would show up as a difference in how
long the cells live and not the number of population doublings.
> Now this seems to me to be the most solid evidence, except I still
> wonder: could tumor cells have requirements for metabolism that
> are in _some_ respects less demanding than normal cells?
To me, cancerous cell would be more demanding in terms of metabolism than
normal cells.
Raymond Yeh
