Hi rawmo,
dmt crosses the blood brain barrier (BBB) as a freebase, so if you inject/eat dmt in salt form it will be freebased in the blood before it becomes available to the brain. Note that the pH of the blood is 7.2-7.4. With dmt having a pKa of 8.68, 3.2% to 5% of the dmt in the blood will exist as a freebase. This portion will cross the BBB, then some more of the salty dmt in the blood will get freebased, cross the BBB and so on. Mechanisms that actively facilitate the absorption of dmt may also exist which will increase the rate of its absorption.
Now, in the brain dmt will form salts with whatever anions is around, phosphates, chloride, carbonate, etc etc. We have no control of the latter. In any case however, dmt is not going to interact with a receptor as a salt, but as its freebase form. One reason smoking has such a fast onset is because freebased dmt is carried freebased from the pipe to the lungs to the blood to the brain and straight onto the the receptors.
(Injection of dmt fumarate also has a fast onset, fastest than expected from the normal cycle of freebasing in the blood and BBB crossing, that's why Strassman from his studies speculated that dmt is actively transported through the BBB)
Need to calculate between salts and freebases?
Click here!
Need to calculate freebase or salt percentage at a given pH?
Click here!