Immunological characterization and localization of the Na+/Ca2(+)- exchanger in bovine retina

Haase, Winfried; Friese, Waltraud; Gordon, Robert D.; Müller, Heidi Kaastrup; Cook, Neil J.

doi:10.1523/jneurosci.10-05-01486.1990

“…The antibodies against various epitopes of the exchanger were found to label only rod photoreceptor cells. A similar result was reported by Haase et al (38) using a polyclonal antibody. The exchanger in cone cells, therefore, is either expressed at levels below the sensitivity of the labeling methods used in this study or, more likely, is encoded by a distinct gene.…”

Section: Fig 9 Effect Of Proteolysis On the Ksupporting

confidence: 90%

Structure-Function Relationships and Localization of the Na/Ca-K Exchanger in Rod Photoreceptors

Kim

¹

,

Reid

²

,

Molday

³

1998

Journal of Biological Chemistry

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The structural and functional properties of the bovine rod photoreceptor Na/Ca-K exchanger and its distribution in vertebrate photoreceptor cells were studied using a panel of monoclonal antibodies. Antibodies that bind to distinct epitopes along the large hydrophilic N-terminal segment of the exchanger labeled the extracellular surface of the rod outer segment plasma membrane, whereas antibodies against a large hydrophilic loop between the two membrane domains labeled the intracellular side. Enzymatic deglycosylation studies indicated that the exchanger primarily contains O-linked sialo-oligosaccharides located within the N-terminal domain. Removal of the extracellular domain with trypsin or the large intracellular domain with kallikrein did not alter the Na ؉ -or K ؉ -dependent Ca 2؉ efflux activity of the exchanger when reconstituted into lipid vesicles. Anti-exchanger antibodies were also used to visualize the distribution of the exchanger in the retina by light and electron microscopy. The exchanger was localized to the plasma membrane of rod outer segments. No labeling was observed in the disk membranes, cone photoreceptor cells, or other retinal neurons, and only faint staining was seen in the rod inner segment. These results indicate that the O-linked glycosylated rod Na/ Ca-K exchanger is specifically targeted to the plasma membrane of rod photoreceptors and has a topological organization similar to that reported for the cardiac Na/Ca exchanger. The large intracellular and extracellular domains do not directly function in the transport of ions across the rod outer segment plasma membrane, but instead may play a role in protein-protein interactions that maintain the spatial organization of the exchanger in the plasma membrane or possibly regulate transport activity of the exchanger.

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“…During depolarization, [Ca 2+ ]i in both regions of the cell was raised by opening of voltage-gated Ca 2+ channels, and by reversing the direction of the NCKX exchanger in the OS. As illustrated in Figure 4A, panel b, Ca 2+ extrusion from the OS was blocked by removing Na + from the superfusing solution, consistent with a dominant role for this Ca 2+ extrusion mechanism in the OS (40,46). Na + removal had no effect on Ca 2+ extrusion from the IS.…”

Section: Ca 2+ Extrusion From the Inner Segmentmentioning

confidence: 55%

“…Na + /Ca 2+ , K + exchangers (NCKXs), cloned from photoreceptor OSs, belong to a unique transporter family, distinct from the more generic Na + /Ca 2+ exchangers (NCXs) found in the majority of other neurons. Photoreceptors express the NCKX1 isoform (40)(41). The cloning of NCKX1 from rat eye (42) revealed the presence of alternatively spliced isoforms in this species, which differ in the arrangement of four exons at the N terminus of the large intracellular loop.…”

Section: Ca 2+ Extrusion and Buffering In The Outer Segmentmentioning

confidence: 97%

Calcium regulation in photoreceptors

Križaj

¹

,

Copenhagen

²

2002

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In this review we describe some of the remarkable and intricate mechanisms through which the calcium ion (Ca 2+ ) contributes to detection, transduction and synaptic transfer of light stimuli in rod and cone photoreceptors. The function of Ca 2+ is highly compartmentalized. In the outer segment, Ca 2+ controls photoreceptor light adaptation by independently adjusting the gain of phototransduction at several stages in the transduction chain. In the inner segment and synaptic terminal, Ca 2+ regulates cells' metabolism, glutamate release, cytoskeletal dynamics, gene expression and cell death. We discuss the mechanisms of Ca 2+ entry, buffering, sequestration, release from internal stores and Ca 2+ extrusion from both outer and inner segments, showing that these two compartments have little in common with respect to Ca 2+ homeostasis. We also investigate the various roles played by Ca 2+ as an integrator of intracellular signaling pathways, and emphasize the central role played by Ca 2+ as a second messenger in neuromodulation of photoreceptor signaling by extracellular ligands such as dopamine, adenosine and somatostatin. Finally, we review the intimate link between dysfunction in photoreceptor Ca 2+ homeostasis and pathologies leading to retinal dysfunction and blindness. KeywordsRetina; Photoreceptor; Rod; Cone; Calcium; Plasma Membrane Calcium Atpase; Na-Ca Exchange; Calcium Store; Calcium Buffering; Calcium Channel; Calcium Extrusion; Ryanodine; Inner Segment; Dystrophy; Synaptic Transmission; Review INTRODUCTIONThe calcium ion (Ca 2+ ) is a major messenger for coordinating activity of eukaryote cells. Its extensive distribution and functioning as a control ion is common to a huge range of eukaryote cell types from animal, plant or fungal sources which diverged billions of years ago. The signaling potential of Ca 2+ is linked to the ability of cells to maintain a large concentration gradient between the cytosol (with basal Ca 2+ levels typically ~ 50 nM) and the extracellular media (with Ca 2+ ~ 1.5 mM). Because of this 10,000-fold difference in [Ca 2+ ]i between the cytosol and the extracellular space, Ca 2+ influx across the plasma membrane and Ca 2+ release from intracellular stores may produce large fluctuations of free cytosolic Ca 2+ (1). Another important feature of Ca 2+ homeostasis is that [Ca 2+ ]i elevations in the cell can be highly localized. We now know that the diffusion of Ca 2+ within the cytosol is much slower than that of other intracellular messengers (2,3). Ca 2+ is thus able to regulate a variety of different functions in different parts of the cell. Such selective action of Ca 2+ is facilitated by Ca 2+ -binding proteins which are often localized to specific sites mediating individual functions (4). To understand Ca 2+ signaling, it is therefore essential to map the spatial distribution of Ca 2+ effector proteins such as Ca 2+ channels, Ca 2+ pumps, cytoplasmic buffers and intracellular Anatomically, primary sensory neurons are notable for their compartmentalization into input ...

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“…Another isoform was recently isolated from cones (43). The NCKX1 transporters are expressed exclusively in the OS, with no trace found in the IS (40)(41). The NCKX transporter exchanges 4Na + for one Ca 2+ and one K + (44)(45).…”

Section: Ca 2+ Extrusion and Buffering In The Outer Segmentmentioning

confidence: 99%

Calcium regulation in photoreceptors

Križaj¹

2002

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In this review we describe some of the remarkable and intricate mechanisms through which the calcium ion (Ca 2+ ) contributes to detection, transduction and synaptic transfer of light stimuli in rod and cone photoreceptors. The function of Ca 2+ is highly compartmentalized. In the outer segment, Ca 2+ controls photoreceptor light adaptation by independently adjusting the gain of phototransduction at several stages in the transduction chain. In the inner segment and synaptic terminal, Ca 2+ regulates cells' metabolism, glutamate release, cytoskeletal dynamics, gene expression and cell death. We discuss the mechanisms of Ca 2+ entry, buffering, sequestration, release from internal stores and Ca 2+ extrusion from both outer and inner segments, showing that these two compartments have little in common with respect to Ca 2+ homeostasis. We also investigate the various roles played by Ca 2+ as an integrator of intracellular signaling pathways, and emphasize the central role played by Ca 2+ as a second messenger in neuromodulation of photoreceptor signaling by extracellular ligands such as dopamine, adenosine and somatostatin. Finally, we review the intimate link between dysfunction in photoreceptor Ca 2+ homeostasis and pathologies leading to retinal dysfunction and blindness. KeywordsRetina; Photoreceptor; Rod; Cone; Calcium; Plasma Membrane Calcium Atpase; Na-Ca Exchange; Calcium Store; Calcium Buffering; Calcium Channel; Calcium Extrusion; Ryanodine; Inner Segment; Dystrophy; Synaptic Transmission; Review INTRODUCTIONThe calcium ion (Ca 2+ ) is a major messenger for coordinating activity of eukaryote cells. Its extensive distribution and functioning as a control ion is common to a huge range of eukaryote cell types from animal, plant or fungal sources which diverged billions of years ago. The signaling potential of Ca 2+ is linked to the ability of cells to maintain a large concentration gradient between the cytosol (with basal Ca 2+ levels typically ~ 50 nM) and the extracellular media (with Ca 2+ ~ 1.5 mM). Because of this 10,000-fold difference in [Ca 2+ ]i between the cytosol and the extracellular space, Ca 2+ influx across the plasma membrane and Ca 2+ release from intracellular stores may produce large fluctuations of free cytosolic Ca 2+ (1). Another important feature of Ca 2+ homeostasis is that [Ca 2+ ]i elevations in the cell can be highly localized. We now know that the diffusion of Ca 2+ within the cytosol is much slower than that of other intracellular messengers (2,3). Ca 2+ is thus able to regulate a variety of different functions in different parts of the cell. Such selective action of Ca 2+ is facilitated by Ca 2+ -binding proteins which are often localized to specific sites mediating individual functions (4). To understand Ca 2+ signaling, it is therefore essential to map the spatial distribution of Ca 2+ effector proteins such as Ca 2+ channels, Ca 2+ pumps, cytoplasmic buffers and intracellular Anatomically, primary sensory neurons are notable for their compartmentalization into input ...

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Immunological characterization and localization of the Na+/Ca2(+)- exchanger in bovine retina

Cited by 26 publications

References 37 publications

Structure-Function Relationships and Localization of the Na/Ca-K Exchanger in Rod Photoreceptors

Structure-Function Relationships and Localization of the Na/Ca-K Exchanger in Rod Photoreceptors

Calcium regulation in photoreceptors

Calcium regulation in photoreceptors

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