Energy output of mitochondria located near synaptic ribbons in inner ear hair cells

Abstract

The mitochondrion plays an essential role in every cell. ATP, the primary energy source in the body, is produced by ATP synthase molecules located in the cristae of the mitochondria. In this study, we utilized EM tomography to create 3D models of mitochondrial cristae from hair cells in the vestibular nervous system. Analyzing these models provided insight into the role of these cristae in activity near ribbon synapses and synaptic vesicles. When action potentials reach nerve terminals, synaptic vesicles fuse with the membrane, releasing neurotransmitters. After this, the vesicles are quickly reinternalized and refilled with neurotransmitters through endocytosis, which requires ATP (Guatimosim and von Gersdorff, 2002). In this study, we wanted to determine whether ribbon synapses and their vesicles utilized large amounts of energy from adjacent mitochondria to transmit signals. Our calculations of energy output in this mitochondrion with lamellar‐shaped cristae yielded estimates of ATP production of about 1000 zeptomoles/sec and energy production at 25–30 femtojoules, consistent with other hair cell mitochondria of similar size. Using the 3D models that we constructed, we also counted the number of crista junctions (CJs), the locations where the crista meets the inner membrane of the mitochondria, and observed that the ratio of CJs facing the ribbon synapse to those facing away was approximately 1:1. We concluded that there was no relationship between the location of the crista junctions and that of the ribbon synapse.Support or Funding InformationSupported by NIH R21‐DC013181 (AL) and P41‐RR004050 (GP, ME).