E-Conference: Defining Calcium Entry Signals
CRAC activity at low agonist concentrations?
16 June 2004
The experiments with subthreshold agonist concentrations were done with fura-2 in intact cells and in patch-clamp experiments. Of course, the fura -2 data only imply that CRAC is responsible for the observed increase in [Ca2+]i. In the patch-clamp experiments, there is no detectable increase in current (that's the nature of CRAC under unbuffered conditions). So yes, we have no absolute proof that the signal we observe is indeed due to CRAC.
However, I would like to point out that we have never seen an agonist - induced current under buffered conditions other than CRAC. We tried hard to find ARC, but so far have never seen it.
I realize that you state you have seen ARC currents in RBL cells (as unpublished observations), but we have not been able to get a 0.5-pA/pF increase, even with high CCh (carbachol) concentrations on top of IP3-induced CRAC. (We have not tried this with low CCh concentrations, but I can't see why high CCh would fail to activate ARC under buffered [Ca2+]i.)
So, if you have an RBL cell line that produces a robust ARC, I would certainly be interested in getting it.
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