What tissues or cells are you using it on? How are you assessing its effect? I've used it on isolated mouse skeletal muscle (i.e., soleus). It worked incredibly fast (i.e., in less than 30 seconds) and completely (i.e., contractile force reduced to zero). I used a bath concentration of 1 µM. However, it has been over 20 years since I did those experiments so I don't remember all of the details.

@Gordon L Warren

I am using it on NSC derived neurons.

Dear Yojet,

I suppose you have patch clamp rig to measure ionic currents, if yes, then you can simply patch NSC derived neuron and record inward INa and apply TTX. You shall see rapid and almost complete block of sodium currents (see attached pic) which will confirm the efficacy and potency of TTX stocks you have. You can refer to the following paper for internal external combination and protocol to be used for recording.

Article Endothelin-1 Decreases Excitability of the Dorsal Root Gangl...

Ensure that you aliquote your TTX and store it at -20/80 to preserves its efficacy. I hope it helps!

Best,

Nand

A straightforward alternative to patching would be by calcium imaging (e.g. with Fluo-4).