Gating of Ca super(2+)-Activated K super(+) Channels Controls Fast Inhibitory Synaptic Transmission at Auditory Outer Hair Cells

Fast inhibitory synaptic transmission in the central nervous system is mediated by ionotropic GABA or glycine receptors. Auditory outer hair cells present a unique inhibitory synapse that uses a Ca super(2+)-permeable excitatory acetylcholine receptor to activate a hyperpolarizing potassium current mediated by small conductance calcium-activated potassium (SK) channels. It is shown here that unitary inhibitory postsynaptic currents at this synapse are mediated by SK2 channels and occur rapidly, with rise and decay time constants of similar to 6 ms and similar to 30 ms, respectively. This time course is determined by the Ca super(2+) gating of SK channels rather than by the changes in intracellular Ca super(2+). The results demonstrate fast coupling between an excitatory ionotropic neurotransmitter receptor and an inhibitory ion channel and imply rapid, localized changes in subsynaptic calcium levels.