scholarly journals Calcium flares and compartmentalization in rod photoreceptors

2020 ◽  
Vol 117 (35) ◽  
pp. 21701-21710 ◽  
Author(s):  
Yunzhen Li ◽  
Fabio Falleroni ◽  
Simone Mortal ◽  
Ulisse Bocchero ◽  
Dan Cojoc ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Intracellular Calcium ◽  
Outer Segment ◽  
Near Infrared ◽  
Fundamental Aspect ◽  
Calcium Dynamics ◽  
Rod Photoreceptors ◽  
Functional Gradient ◽  
Bright Flash

Rod photoreceptors are composed of a soma and an inner segment (IS) connected to an outer segment (OS) by a thin cilium. OSs are composed of a stack of ∼800 lipid discs surrounded by the plasma membrane where phototransduction takes place. Intracellular calcium plays a major role in phototransduction and is more concentrated in the discs, where it can be incorporated and released. To study calcium dynamics in rods, we used the fluorescent calcium dye CaSiR-1 AM working in the near-infrared (NIR) (excitation at 650 and emission at 664 nm), an advantage over previously used dyes. In this way, we investigated calcium dynamics with an unprecedented accuracy and most importantly in semidark-adapted conditions. We observed light-induced drops in [Ca2+]iwith kinetics similar to that of photoresponses recorded electrophysiologically. We show three properties of the rods. First, intracellular calcium and key proteins have concentrations that vary from the OS base to tip. At the OS base, [Ca2+]iis ∼80 nM and increases up to ∼200 nM at the OS tip. Second, there are spontaneous calcium flares in healthy and functional rod OSs; these flares are highly localized and are more pronounced at the OS tip. Third, a bright flash of light at 488 nm induces a drop in [Ca2+]iat the OS base but often a flare at the OS tip. Therefore, rod OSs are not homogenous structures but have a structural and functional gradient, which is a fundamental aspect of transduction in vertebrate photoreceptors.

scholarly journals Immunocytochemical localization of opsin in the cell membrane of developing rat retinal photoreceptors.

1984 ◽  
Vol 98 (5) ◽  
pp. 1788-1795 ◽  
Author(s):  
I Nir ◽  
D Cohen ◽  
D S Papermaster
Keyword(s):  
Plasma Membrane ◽  
Outer Segment ◽  
Plasma Membranes ◽  
Photoreceptor Cells ◽  
Rod Photoreceptor ◽  
Rod Photoreceptors ◽  
Retinal Photoreceptors ◽  
Retinal Rod ◽  
Ros Formation ◽  
Developing Rat

Mature retinal rod photoreceptors sequester opsin in the disk and plasma membranes of the rod outer segment (ROS). Opsin is synthesized in the inner segment and is transferred to the outer segment along the connecting cilium that joins the two compartments. We have investigated early stages of retinal development during which the polarized distribution of opsin is established in the rod photoreceptor cell. Retinas were isolated from newborn rats, 3-21 d old, and incubated with affinity purified biotinyl-sheep anti-bovine opsin followed by avidin-ferritin. At early postnatal ages prior to the development of the ROS, opsin is labeled by antiopsin on the inner segment plasma membrane. At the fifth postnatal day, as ROS formation begins opsin was detected on the connecting cilium plasma membrane. However, the labeling density of the ciliary plasma membrane was not uniform: the proximal cilium was relatively unlabeled in comparison with the distal cilium and the ROS plasma membrane. In nearly mature rat retinas, opsin was no longer detected on the inner segment plasma membrane. A similar polarized distribution of opsin was also observed in adult human rod photoreceptor cells labeled with the same antibodies. These results suggest that some component(s) of the connecting cilium and its plasma membrane may participate in establishing and maintaining the polarized distribution of opsin.

scholarly journals A derivative of amiloride blocks both the light-regulated and cyclic GMP-regulated conductances in rod photoreceptors.

1987 ◽  
Vol 90 (5) ◽  
pp. 651-669 ◽  
Author(s):  
G D Nicol ◽  
P P Schnetkamp ◽  
Y Saimi ◽  
E J Cragoe ◽  
M D Bownds
Keyword(s):  
Plasma Membrane ◽  
Cyclic Gmp ◽  
Dark Current ◽  
Outer Segment ◽  
Light Response ◽  
Ionic Channels ◽  
Rod Photoreceptors ◽  
Low Concentrations ◽  
Excised Patches ◽  
Activated Flux

Vertebrate rod photoreceptors in the dark maintain an inward current across the outer segment membrane. The photoresponse results from a light-induced suppression of this dark current. The light-regulated current is not sensitive to either tetrodotoxin or amiloride, potent blockers of Na+ channels. Here, we report that a derivative of amiloride, 3',4'-dichlorobenzamil (DCPA), completely suppresses the dark current and light response recorded from rod photoreceptors. DCPA also blocks a cyclic GMP-activated current in excised patches of rod plasma membrane and a cGMP-induced Ca++ flux from rod disk membranes. These results are consistent with the notion that the Ca++ flux mechanism in the disk membrane and the light-regulated conductance in the plasma membrane are identical. DCPA also inhibits the Na/Ca exchange mechanism in intact rods, but at a 5-10-fold-higher concentration than is required to block the cGMP-activated flux and current. The blocking action of DCPA in 10 nM Ca++ is different from that in 1 mM Ca++, which suggests either that the conductance state of the light-regulated channel may be modified in high and low concentrations of Ca++, or that there may be two ionic channels in the rod outer segment membrane.

scholarly journals Rod disc renewal occurs by evagination of the ciliary plasma membrane that makes cadherin-based contacts with the inner segment

2015 ◽  
Vol 112 (52) ◽  
pp. 15922-15927 ◽  
Author(s):  
Thomas Burgoyne ◽  
Ingrid P. Meschede ◽  
Jemima J. Burden ◽  
Maryse Bailly ◽  
Miguel C. Seabra ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Plasma Membrane ◽  
Fusion Proteins ◽  
Outer Segment ◽  
Actin Polymerization ◽  
Electron Tomography ◽  
Rod Photoreceptors ◽  
Immuno Electron Microscopy ◽  
Leading Edges ◽  
Membrane Fusion Proteins

The outer segments of vertebrate rod photoreceptors are renewed every 10 d. Outer segment components are transported from the site of synthesis in the inner segment through the connecting cilium, followed by assembly of the highly ordered discs. Two models of assembly of discrete discs involving either successive fusion events between intracellular rhodopsin-bearing vesicles or the evagination of the plasma membrane followed by fusion of adjacent evaginations have been proposed. Here we use immuno-electron microscopy and electron tomography to show that rhodopsin is transported from the inner to the outer segment via the ciliary plasma membrane, subsequently forming successive evaginations that “zipper” up proximally, but at their leading edges are free to make junctions containing the protocadherin, PCDH21, with the inner segment plasma membrane. Given the physical dimensions of the evaginations, coupled with likely instability of the membrane cortex at the distal end of the connecting cilium, we propose that the evagination occurs via a process akin to blebbing and is not driven by actin polymerization. Disassembly of these junctions is accompanied by fusion of the leading edges of successive evaginations to form discrete discs. This fusion is topologically different to that mediated by the membrane fusion proteins, SNAREs, as initial fusion is between exoplasmic leaflets, and is accompanied by gain of the tetraspanin rim protein, peripherin.

A SIMPLE MODEL FOR INTERACTION OF VOLTAGE AND CALCIUM DYNAMICS IN VIRTUAL VENTRICULAR TISSUE

2003 ◽  
Vol 13 (12) ◽  
pp. 3873-3886
Author(s):  
O. V. ASLANIDI ◽  
A. V. HOLDEN
Keyword(s):  
Intracellular Calcium ◽  
Calcium Release ◽  
Cell Model ◽  
Excitation Threshold ◽  
Calcium Dynamics ◽  
Variable Model ◽  
Ventricular Cell ◽  
Calcium Dependent ◽  
Intracellular Ca ◽  
A Site

A simple two-variable model is used to replace the formulation of calcium dynamics in the Luo–Rudy ventricular cell model. Virtual ventricular cell and tissue are developed and validated to reproduce restitution properties and calcium-dependent voltage patterns present in the original model. Basic interactions between the membrane potential and Ca 2+ dynamics in the virtual cell and a strand of the virtual tissue are studied. Intracellular calcium waves can be linked to both action potentials (APs) and delayed afterdepolarizations (DADs). An intracellular calcium wave propagating from the cell interior can induce an AP upon reaching the cell membrane. The voltage and the intracellular Ca 2+ patterns within the same cell can be highly desynchronized. In a one-dimensional strand of the virtual tissue calcium motion is driven by the AP propagation. However, calcium release can be induced upon certain conditions (e.g. Na + overload of the cells), which results in DADs propagating in the wake of AP. Such propagating DADs can reach the excitation threshold, generating a pair of extrasystolic APs. Collision of a propagating AP with a site of elevated intracellular Ca 2+ concentration does not affect the propagation under the normal conditions. Under Na + overload local elevation of the intracellular Ca 2+ leads to generation of an extrasystolic AP, which destroys the original propagating AP.

scholarly journals Modulation of calcium signaling depends on the oligosaccharide of GM1 in Neuro2a mouse neuroblastoma cells

2020 ◽  
Vol 37 (6) ◽  
pp. 713-727
Author(s):  
Giulia Lunghi ◽  
Maria Fazzari ◽  
Erika Di Biase ◽  
Laura Mauri ◽  
Sandro Sonnino ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Calcium Channels ◽  
Calcium Signaling ◽  
Intracellular Calcium ◽  
Calcium Imaging ◽  
Neuroblastoma Cells ◽  
Ganglioside Gm1 ◽  
Mouse Neuroblastoma ◽  
Neuro2a Cells ◽  
Neuronal Functions

AbstractRecently, we demonstrated that the oligosaccharide portion of ganglioside GM1 is responsible, via direct interaction and activation of the TrkA pathway, for the ability of GM1 to promote neuritogenesis and to confer neuroprotection in Neuro2a mouse neuroblastoma cells. Recalling the knowledge that ganglioside GM1 modulates calcium channels activity, thus regulating the cytosolic calcium concentration necessary for neuronal functions, we investigated if the GM1-oligosaccharide would be able to overlap the GM1 properties in the regulation of calcium signaling, excluding a specific role played by the ceramide moiety inserted into the external layer of plasma membrane. We observed, by calcium imaging, that GM1-oligosaccharide administration to undifferentiated Neuro2a cells resulted in an increased calcium influx, which turned out to be mediated by the activation of TrkA receptor. The biochemical analysis demonstrated that PLCγ and PKC activation follows the TrkA stimulation by GM1-oligosaccharide, leading to the opening of calcium channels both on the plasma membrane and on intracellular storages, as confirmed by calcium imaging experiments performed with IP3 receptor inhibitor. Subsequently, we found that neurite elongation in Neuro2a cells was blocked by subtoxic administration of extracellular and intracellular calcium chelators, suggesting that the increase of intracellular calcium is responsible of GM1-oligosaccharide mediated differentiation. These results suggest that GM1-oligosaccharide is responsible for the regulation of calcium signaling and homeostasis at the base of the neuronal functions mediated by plasma membrane GM1.

scholarly journals Agonist-induced Ca2+ influx in human neutrophils is secondary to the emptying of intracellular calcium stores

1991 ◽  
Vol 277 (1) ◽  
pp. 73-79 ◽  
Author(s):  
M Montero ◽  
J Alvarez ◽  
J Garcia-Sancho
Keyword(s):  
Plasma Membrane ◽  
Intracellular Calcium ◽  
Time Course ◽  
Human Neutrophils ◽  
Calcium Stores ◽  
Free Medium ◽  
Prolonged Incubation ◽  
Intracellular Calcium Stores ◽  
Cytochrome P 450 ◽  
In Cells

Emptying of the intracellular calcium stores of human neutrophils, by prolonged incubation in Ca(2+)-free medium, by treatment with low concentrations of the Ca2+ inophore ionomycin, or by activation with cell agonists, increased the plasma-membrane permeability to Ca2+ and Mn2+. The chemotactic peptide formylmethionyl-leucyl-phenylalanine and the natural agonists platelet-activating factor and leukotriene B4 released different amounts of calcium from the stores and induced Ca2+ (Mn2+) uptake, the rate of which correlated inversely with the amount of calcium left in the stores. The increased Mn2+ uptake induced by these agonists was persistent in cells incubated in Ca(2+)-free medium, but returned to basal levels in cells incubated in Ca(2+)-containing medium, with the same time course as the refilling of the calcium stores. The calcium-stores-regulated Mn2+ influx, including that induced by agonists, was prevented by cytochrome P-450 inhibitors. We propose that agonist-induced Ca2+ (Mn2+) influx in human neutrophils is secondary to the emptying of the intracellular stores which, in turn, activates plasma-membrane Ca2+ channels by a mechanism involving microsomal cytochrome P-450, similar to that described previously in thymocytes [Alvarez, Montero & Garcia-Sancho (1991) Biochem. J. 274, 193-197].

Sign in / Sign up

Export Citation Format

Share Document