That's true, thanks for pointing that out! Strassman just make a speculation about the active transportation of dmt, maybe trying to further glorify its effects in the brain I think.

Very true is also the note that protonated forms can bind to receptors, what does not happen is actually a dmt-anion complex binding to the receptor. Receptor binding sites do not usually have enough space (or favourable environment) to accommodate whole salt complexes. And in practise a ligand binding to receptor is stabilised by all sorts of interactions that may (or may not) involve local protonation of the prospective ligand.

Long story short, it's just the dmt molecule (protonated or not) that binds on the receptor(s) and exerts its effects.