Ultrastructural localization of calcium homeostasis modulator 1 in the taste buds of mouse circumvallate papillae

Taste receptor cells are morphologically classified as types II and III. These two types of cells transduce different taste modalities and form morphologically distinct synapses with afferent nerve fibers. Type III cells form conventional chemical synapses, whereas type II cells form a unique type of synapses referred to as channel synapses, which release adenosine triphosphate (ATP) as a neurotransmitter through voltage-gated channels comprising calcium homeostasis modulator (CALHM) 1 and CALHM3. Further, channel synapses are associated with large mitochondria with tubular cristae known as atypical mitochondria, which are believed to produce ATP for neurotransmission. Herein, we aimed to generate a monoclonal antibody against CALHM1 and examine its localization in taste buds using immunoelectron microscopy. CALHM1 was detected along the plasma membrane apposed to atypical mitochondria, indicating that CALHM1 is localized at the presynaptic membrane of channel synapses. Additionally, CALHM1 was detected along the plasma membrane lined by subsurface cisternae at sites apposed to afferent nerve fibers.