On Thu, 31 Aug 1995, VIVIAN F F WU wrote:
> Question: Would dissolving Monensin in DMSO and adding 1-5 uM of it into
> mononuclear cell cultures for < 24 hours affect the integrity of the cell
> surface antigens?
Yes, it would! Monensin is a monovalent cation ionophore. Under
physiological cation concentrations in cytoplasm and outside, it moves
sodium in and potassium (although less of it) out. These ion movements
across the membrane lead to changes of transmembrane potential (mostly
depolarization). This by itself can change the expression of certain
surface antigens (Thy-1 and CD2 for example). More important is that in many
systems including lymphocytes depolarization effects in calcium influx
into the cytoplasm and thus can activate Ca-dependent mechanisms
(Ca-calmodulin - dependent kinases and even -to some extent- PKC. This
may lead to many activation-like changes on the cell surface.
>
> Question: At what strength does Monensin ceases to become toxic?
In our experience Monensin concentrations below 1 uM produced desired ion
fluxes, while keeping more than 90% of cells alive for up to 6 hours. We
did not try longer incubations. The trick is not to exceed the cell's
capacity to overcome noxious cation fluctuations, which is done by
ATP-dependent membrane pumps. These are not very active in mononuclear
blood cells though!
Hope this helps-
Jacek M. Witkowski MD, PhD.
Flow Cytometry Lab,
Molecular Immunology Group
Department of Histology and Immunology
Medical University of Gdansk, Poland