Rafts are defined as short lived, small (this is the problem, nobody have established how small) plasmamalemma proper microdomains, that starting from 2000 and up are doing everything in a cell. Therefore, are caveolae rafts or not?
Not necessarily, as caveolae are plasma invaginations formed by caveolin proteins for endocytosis, whereas rafts are plain nanodomains floating freely on cell surface, spanning entire membrane and consisting of outer and inner leaflet glued by cholesterol. Rafts represent ordered lipid bilayer with surface and integral proteins embeded and crucial for cell signaling.
Therefore, caveolae are not rafts, because they are not floating freely on the sea of plasmalemma.
Caveolae are also rich in cholesterol, frequently found in different cell types e.g. keratinocytes, smooth muscle or endothelial cells. Although the term lipid rafts (LR) is usually addressed to any nanodomain enriched with cholesterol (plain or invaginated), the meaning of the term point to plain nanodomians. For me, one who talks about caveolae should'nt confused others that he actually talks about LR and vice versa...
Do you believe that we should make this point to be clear for evryone: the caveolae are not to be confunded with lr?
That is a very tricky question which has not been completely answered so far.
Caveolae are not exactly rafts as they are invaginated but as they share the same lipidic components, they could be classify as so.
I would classify them as a sub-class of rafts.
And I agree with Dan that LR and caveolea should be clearly defined as there are too many people who are confused or confusing in their papers.
Hi Sylviane,
Thanks, I do believe that what we need is a DEFINITION of rafts, as long as there is no one to fulfil more than one two criteria, the term micro or nano-domain is more appropiate and accurate.Anyhow one more time thanks.
Dear Colleagues, I would like to point you to an articel (2007), in which the following (on p. 870) is stressed:
==> REVIEW: Lipid rafts: dream or reality for cholesterol transporters?
Stéphane Orlowski · Christine Coméra ·François Tercé · Xavier Collet
Eur Biophys J (2007) 36:869–885, DOI 10.1007/s00249-007-0193-8
Best wishes and regards, Wolfgang Muß, Salzburg-Austria
Hi Dr. Muss,
Thank you for your response, it has a point on it. However, there is no doubt that there are lipid rafts in the membranes of any cell, this is a fact that cant be denied. The problem is that they are defined as short lived entities and by no means the caveolae are short lived. So, without a clear definition what are the lipid rafts, or much better how to define them to corespond to the biological reality. In conclusion either we accept that there are short lived and stable (long lived, just to use the terminology from definition) raft and therefore the caveolae could be seen as stable lipid raft or they are shor lived and the caveolae are not lipid rafts. One more time thanks for your involvement and for the reference.
Regards
Dan P
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