Tuesday, May 12, 2009

alpha & beta intercalated cells of the collecting duct

Heard a great talk today from the 2007 recipient of the Homer Smith Award & editor of Kidney International: Qais Al-Awqati of Columbia. The full details of much of the talk can be found in this JASN article describing his acceptance talk at the ASN, but I will attempt to paraphrase.

The collecting duct has two types of cells: principal cells (the aldosterone-responsive, ENac-expressing cells which also mediate water reabsorption via ADH) and the intercalated cells. The intercalated cells come in two different varieties: alpha-intercalated cells (which secrete acid) and beta-intercalated cells (which secrete base). The alpha-intercalated cells (on the left in the figure) are tall, columnar epithelial cells which contain apical H+ ATPase, explaining its ability to secrete protons. The beta-intercalated cells (on the right) in contrast are shorter, flatter cells which contain an apical chloride-bicarbonate exchanger (called pendrin) which enables it to secrete base.
The interesting thing is that inducing metabolic acidosis results in the conversion of beta-intercalated cells to alpha-intercalated cells--giving the kidney a greater ability to secrete protons and return pH to the normal range. This conversion event is regulated by a secreted extracellular matrix molecule called hensin. Since these cells evidently retain the ability to switch between markedly different cellular phenotypes, it has become of interest to the ever-evolving field of stem cell biology.


transplanted said...

Correction: metabolic acidosis causes conversion of beta cells into alfa intercalated cells (vice-versa is stated in your note) so more protons are excreted. In steady state, beta cells are minimally active since there is no need to excrete base.

nathanhellman said...

Thanks for pointing out my typo! I've made the change. Cheers.