One transmits notes about currency (6)
I believe the answer is:
neuron
'one transmits' is the definition.
(nerve cell transmitting electrical signals)
'notes about currency' is the wordplay.
'notes' becomes 'nn' (I've seen this in other clues).
'about' indicates putting letters inside.
'currency' becomes 'euro' (I've seen this before).
'nn' enclosing 'euro' is 'NEURON'.
(Other definitions for neuron that I've seen before include "Part of one's nervous system" , "Conductor" , "that makes for nervous transmission" , "Nerve impulse cell" , "Impulsive thing" .)