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Full-Text Articles in Medicine and Health Sciences
Ca2+ Diffusion Through Endoplasmic Reticulum Supports Elevated Intraterminal Ca2+ Levels Needed To Sustain Synaptic Release From Rods In Darkness., Minghui Chen, Matthew J. Van Hook, Wallace B. Thoreson
Ca2+ Diffusion Through Endoplasmic Reticulum Supports Elevated Intraterminal Ca2+ Levels Needed To Sustain Synaptic Release From Rods In Darkness., Minghui Chen, Matthew J. Van Hook, Wallace B. Thoreson
Journal Articles: Ophthalmology
UNLABELLED: In addition to vesicle release at synaptic ribbons, rod photoreceptors are capable of substantial slow release at non-ribbon release sites triggered by Ca(2+)-induced Ca(2+) release (CICR) from intracellular stores. To maintain CICR as rods remain depolarized in darkness, we hypothesized that Ca(2+) released into the cytoplasm from terminal endoplasmic reticulum (ER) can be replenished continuously by ions diffusing within the ER from the soma. We measured [Ca(2+)] changes in cytoplasm and ER of rods from Ambystoma tigrinum retina using various dyes. ER [Ca(2+)] changes were measured by loading ER with fluo-5N and then washing dye from the cytoplasm with …
A Positive Feedback Synapse From Retinal Horizontal Cells To Cone Photoreceptors., Skyler L. Jackman, Norbert Babai, James J. Chambers, Wallace B. Thoreson, Richard H. Kramer
A Positive Feedback Synapse From Retinal Horizontal Cells To Cone Photoreceptors., Skyler L. Jackman, Norbert Babai, James J. Chambers, Wallace B. Thoreson, Richard H. Kramer
Journal Articles: Ophthalmology
Cone photoreceptors and horizontal cells (HCs) have a reciprocal synapse that underlies lateral inhibition and establishes the antagonistic center-surround organization of the visual system. Cones transmit to HCs through an excitatory synapse and HCs feed back to cones through an inhibitory synapse. Here we report that HCs also transmit to cone terminals a positive feedback signal that elevates intracellular Ca(2+) and accelerates neurotransmitter release. Positive and negative feedback are both initiated by AMPA receptors on HCs, but positive feedback appears to be mediated by a change in HC Ca(2+), whereas negative feedback is mediated by a change in HC membrane …
Calcium Regulates Vesicle Replenishment At The Cone Ribbon Synapse., Norbert Babai, Theodore M. Bartoletti, Wallace B. Thoreson
Calcium Regulates Vesicle Replenishment At The Cone Ribbon Synapse., Norbert Babai, Theodore M. Bartoletti, Wallace B. Thoreson
Journal Articles: Ophthalmology
Cones release glutamate-filled vesicles continuously in darkness, and changing illumination modulates this release. Because sustained release in darkness is governed by vesicle replenishment rates, we analyzed how cone membrane potential regulates replenishment. Synaptic release from cones was measured by recording postsynaptic currents in Ambystoma tigrinum horizontal or OFF bipolar cells evoked by depolarization of simultaneously voltage-clamped cones. We measured replenishment after attaining a steady state between vesicle release and replenishment using trains of test pulses. Increasing Ca(2+) currents (I(Ca)) by changing the test step from -30 to -10 mV increased replenishment. Lengthening -30 mV test pulses to match the Ca(2+) …
Calcium Homeostasis And Cone Signaling Are Regulated By Interactions Between Calcium Stores And Plasma Membrane Ion Channels., Tamas Szikra, Peter Barabas, Theodore M. Bartoletti, Wei Huang, Abram Akopian, Wallace B. Thoreson, David Krizaj
Calcium Homeostasis And Cone Signaling Are Regulated By Interactions Between Calcium Stores And Plasma Membrane Ion Channels., Tamas Szikra, Peter Barabas, Theodore M. Bartoletti, Wei Huang, Abram Akopian, Wallace B. Thoreson, David Krizaj
Journal Articles: Ophthalmology
Calcium is a messenger ion that controls all aspects of cone photoreceptor function, including synaptic release. The dynamic range of the cone output extends beyond the activation threshold for voltage-operated calcium entry, suggesting another calcium influx mechanism operates in cones hyperpolarized by light. We have used optical imaging and whole-cell voltage clamp to measure the contribution of store-operated Ca(2+) entry (SOCE) to Ca(2+) homeostasis and its role in regulation of neurotransmission at cone synapses. Mn(2+) quenching of Fura-2 revealed sustained divalent cation entry in hyperpolarized cones. Ca(2+) influx into cone inner segments was potentiated by hyperpolarization, facilitated by depletion of …