title: Regulation of presynaptic calcium in a mammalian synaptic terminal.
abstract: Ca(2+) signaling in synaptic terminals plays a critical role in neurotransmitter release and short-term synaptic plasticity. In the present study, we examined the role of synaptic Ca(2+) handling mechanisms in the synaptic terminals of mammalian rod bipolar cells, neurons that play a pivotal role in the high-sensitivity vision pathway. We found that mitochondria sequester Ca(2+) under conditions of high Ca(2+) load, maintaining intraterminal Ca(2+) near resting levels. Indeed, the effect of the mitochondria was so powerful that the ability to clamp intraterminal Ca(2+) with a somatically positioned whole cell patch pipette was compromised. The plasma membrane Ca(2+)-ATPase (PMCA), but not the Na(+)/Ca(2+) exchanger (NCX) or the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA), was an important regulator of resting Ca(2+). Furthermore, PMCA activity, but not NCX or SERCA activity, was essential for the recovery of Ca(2+) levels following depolarization-evoked Ca(2+) entry. Loss of PMCA function was also associated with impaired restoration of membrane surface area following depolarization-evoked exocytosis. Given its roles in the regulation of intraterminal Ca(2+) at rest and after a stimulus-evoked Ca(2+) rise, the PMCA is poised to modulate luminance coding and adaptation to background illumination in the mammalian rod bipolar cell.
authors.affiliation: Department of Neurobiology and Anatomy, University of Texas Medical School at Houston, Houston, TX 77030, USA.
authors.forename: Qun-Fang
authors.initials: QF
authors.lastname: Wan
authors.forename: Everett
authors.initials: E
authors.lastname: Nixon
authors.forename: Ruth
authors.initials: R
authors.lastname: Heidelberger
mesh_terms: D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D005089:Exocytosis; D006054:Goldfish; D051379:Mice; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000378:metabolism; D053499:Plasma Membrane Calcium-Transporting ATPases / Q000378:metabolism; D017729:Presynaptic Terminals / Q000378:metabolism*; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000378:metabolism
chemical_list: D019831:Sodium-Calcium Exchanger; D053499:Plasma Membrane Calcium-Transporting ATPases; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium