A novel membrane contact site in vestibular hair cells
The mammalian vestibular system has two types of sensory receptor hair cells (HCs), each with different neurotransmission mechanisms. Type II HCs use ribbon synapses to transmit neurotransmitters like glutamate to afferent neurons. On the other hand, type I HCs are nearly engulfed by a calyceal afferent ending and also form ribbon synapses. These HCs regulate afferent activity through non-quantal transmission (NQT), which is faster than classic neurotransmitter release and may play a key role in stabilizing vision and balance during rapid head movements. Here, we describe a novel striated contact, present between the mouse type I HC and its calyceal afferent ending, and intimately associated with atypical plasma membrane-apposed (PMA) mitochondria. This distinctive arrangement has the potential to serve or modulate NQT.