Evidence that protons act as neurotransmitters at vestibular hair cell-calyx afferent synapses.
Present data support the conclusion that protons serve as an important neurotransmitter to convey excitatory stimuli from inner ear type I vestibular hair cells to postsynaptic calyx nerve terminals. Time-resolved pH imaging revealed stimulus-evoked extrusion of protons from hair cells and a subsequent buildup of [H(+)] within the confined chalice-shaped synaptic cleft (ΔpH ∼ -0.2). Whole-cell voltage-clamp recordings revealed a concomitant nonquantal excitatory postsynaptic current in the calyx terminal that was causally modulated by cleft acidification. The time course of [H(+)] buildup limits the speed of this intercellular signaling mechanism, but for tonic signals such as gravity, protonergic transmission offers a significant metabolic advantage over quantal excitatory postsynaptic currents--an advantage that may have driven the proliferation of postsynaptic calyx terminals in the inner ear vestibular organs of contemporary amniotes.
Marine Biological Laboratory, Woods Hole, MA 02543.
Stephen M
SM
Highstein
Gay R
GR
Holstein
Mary Anne
MA
Mann
Richard D
RD
Rabbitt
D018069:Hair Cells, Vestibular / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D011522:Protons
D018377:Neurotransmitter Agents; D011522:Protons
indefatigable; synaptic transmission