Signal Transduction in Endothelium: Mechano-Sensing, Ion Channels and Intracellular Calcium

Re^2: Poster0242: B. Nilius

Paul Fransen

On Thu Dec 10, Bernd Nilius wrote
>On Thu Dec 10, Paul Fransen wrote
>>Dr. Nilius,
>>Congratulations with the session and the presentation. In your presentation, you showed that chloride channels play an important role in determining the resting membrane potential and hence may influence Ca-signalling. In our work on endocardial endothelial cells, we also found an important contribution of external chloride in determining Vm, but we also observed an important effect of internal chloride, which suggested that there might be a complex interaction between internal and external chloride in Ca-signalling of endothelial cells (Fransen and Sys, 1997). Do you or does anyone else have an idea about effects of internal chloride on Ca-release as has been demonstrated for monovalent cations (Wood and Gillespie, Cardiovasc. Res. 37: 263-270, 1998).  
>The idea is old: Ca release induces a intraluminal negative potential which inhibits Ca release and should be dissipated by a ER K influx orSR Cl efflux. Thus, intracellular Cl could play a role as Gillespie shows. We have tried to see any changes of release by substitution Cli and by using Cl blockers or by overexpressing ClC6, which is
>mainly loctaed in the ER, but no success (published in Biochem J, Buyse et al). It would be very nice to see any convincing evidence for the dissipation story. We had hoped to find a functional substrate for the massive Cl current carried by VRAC.
>>>Gillespie showed an influence of internal monovalent cations on Ca-release in endothelial cells and suggested a possible role of intracellular chloride. We have shown that increasing internal chloride by pipette perfusion activated a background chloride current in endothelial cells, but we could not exclude or confirm a role of internal calcium. In which endothelial cell type did you do the Cli-substitution, Cl blockers or overexpression of ClC6 (Reference Buyse et al., Biochem J. did not include these experiments and was not in endothelial cells). One of the interesting points of your presentation is that endothelial cells of different origin can differently react to agonist- or mechanical stimulation.  Possibly the endocardial endothelial cells in our study are not just another macrovascular endothelial cell type. Did you look for co-localization of ClC6 isoforms with SERCA2b (or SERCA3-Kahn poster 0156)in endothelial cells as your group has done in COS cells?

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