Structural evidence that the Kv4.3 subunit-rich specializations are distinct from
known chemical synapses. A, A CF terminal in the
cerebellar molecular layer establishes an asymmetrical (type I) chemical synapse
(arrow) with a PC spine (s) and several membrane specializations (arrowheads) with
an IN soma. B–D, High-magnification views of a
membrane specialization between a CF terminal and an IN
(B), an asymmetrical (type I) chemical synapse made
on a Purkinje spine (C), a symmetrical (type II)
synaptic junction (D, right), and a punctum adherens
(D, left) on an IN dendrite. The presence of
presynaptic vesicle clustering distinguishes type I and type II synapses from the
CF-IN membrane specializations. Rigid apposition of the presynaptic and postsynaptic
membranes characterizes all types of junctions. Scale bars:
A, 100 nm; B–D,
50 nm (same magnification).