Basal and Physiological Ca2+ Leak from the Endoplasmic Reticulum of Pancreatic Acinar Cells

Lomax, Richard B.; Camello-Almaraz, Cristina; Coppenolle, Fabien Van; Petersen, O. H.; Tepikin, Alexei V.

doi:10.1074/jbc.m201845200

Cited by 116 publications

(119 citation statements)

References 45 publications

(52 reference statements)

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“…The increased permeability to 4-M␣G was consistent with a previous report that RBTs incorporated into planar bilayers and opened by puromycin are permeable to ions (3), and our results were also supported by a recent report that puromycin can release calcium from the RER (4). The permeation of empty RBTs is especially significant in the context of recent studies by Nicchitta and colleagues (5,6), who reported that approximately two-thirds of the 60 S subunits remain bound to translocons after the normal completion of protein translation, thereby constituting a large pool of persistent, translationally inactive RBT complexes.…”

supporting

confidence: 81%

The Permeability of the Endoplasmic Reticulum Is Dynamically Coupled to Protein Synthesis

Roy

Wonderlin

2003

Journal of Biological Chemistry

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Proteins synthesized by the rough endoplasmic reticulum (RER) co-translationally cross the membrane through the pore of a ribosome-bound translocon (RBT) complex. Although this pore is also permeable to small molecules, it is generally thought that barriers to their permeation prevent the cyclical process of protein translation from affecting the permeability of the RER. We tested this hypothesis by culturing Chinese hamster ovary-S cells with inhibitors of protein translation that affect the occupancy of RBTs by nascent proteins and then permeabilizing the plasma membrane and measuring the permeability of the RER to a small molecule, 4-methyl-umbelliferyl-␣-D-glucopyranoside (4-M␣G). The premature or normal release of nascent proteins by puromycin or pactamycin, respectively, increased the permeability of the RER to 4-M␣G by 20-30%. In contrast, inhibition of elongation and the release of nascent proteins by cycloheximide did not increase the permeability, but it prevented the increase in permeability by pactamycin. We conclude that the permeability of the RER is coupled to protein translation by a simple gating mechanism whereby a nascent protein blocks the pore of a RBT during translation, but after release of the nascent protein the pore is permeable to small molecules as long as an empty ribosome remains bound to the translocon.In eukaryotes, secretory and most integral membrane proteins are synthesized by a translationally active 80 S ribosome composed of 60 S and 40 S subunits and bound to a translocon complex, a heteromeric assembly of proteins embedded in the membrane of the rough endoplasmic reticulum (RER) 1 (Fig. 1). Nascent proteins emerging from the exit tunnel of the 60 S subunit co-translationally cross the membrane of the RER by passing through a protein-conducting channel (PCC) in the translocon complex (1). The exit tunnel of the 60 S subunit and the pore of the PCC must be large enough to be permeated by a nascent protein chain, and this pathway is therefore large enough to be permeated by many other small molecules when a ribosome-bound translocon (RBT) is translationally inactive and empty, i.e. the pore is not occupied by a nascent protein.We previously demonstrated (2) that the permeability of RBTs to a small, polar molecule (4-methyl-umbelliferyl-␣-D-glucopyranoside (4-M␣G)) was increased after puromycin, a tRNA analog, prematurely terminated translation and released nascent protein chains from the PCC (path a, Fig 1). The increased permeability to 4-M␣G was consistent with a previous report that RBTs incorporated into planar bilayers and opened by puromycin are permeable to ions (3), and our results were also supported by a recent report that puromycin can release calcium from the RER (4). The permeation of empty RBTs is especially significant in the context of recent studies by Nicchitta and colleagues (5, 6), who reported that approximately two-thirds of the 60 S subunits remain bound to translocons after the normal completion of protein translation, thereby constituting a large pool ...

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supporting

confidence: 81%

The Permeability of the Endoplasmic Reticulum Is Dynamically Coupled to Protein Synthesis

Roy

Wonderlin

2003

Journal of Biological Chemistry

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“…A high Ca 2+ permeability is probably a factor enabling the ER to exert this dual function. In other cells the basal leak of Ca 2+ is unaffected by inhibitors of IP 3 , ryanodine and NAADP receptors [22,23] and probably occurs though separate pathways. However, the established routes for gated release of Ca 2+ may contribute to a physiological leak, since IP 3 R antagonists have been found to reduce Ca 2+ leakage from the ER after SERCA inhibition in intact cells [24][25][26].…”

Section: Discussionmentioning

confidence: 99%

“…Due to a high basal Ca 2+ permeability of the ER, SERCA inhibition results in rapid Ca 2+ depletion, but the nature of this leak is not completely understood [16]. In permeabilized cells clamped at Ca 2+ concentrations close to the basal [Ca 2+ ] i levels SERCA inhibition results in release of Ca 2+ from the ER, which is unaffected by inhibitors of IP 3 , ryanodine and NAADP receptors [22,23]. It was therefore suggested that basal leak occurs through a pathway separate from these receptors [23].…”

Section: Introductionmentioning

confidence: 99%

“…In permeabilized cells clamped at Ca 2+ concentrations close to the basal [Ca 2+ ] i levels SERCA inhibition results in release of Ca 2+ from the ER, which is unaffected by inhibitors of IP 3 , ryanodine and NAADP receptors [22,23]. It was therefore suggested that basal leak occurs through a pathway separate from these receptors [23]. However, in populations of intact cells IP 3 Rs seem to contribute to loss of Ca 2+ from the ER after SERCA inhibition, since loading with the receptor antagonist heparin [24] or exposure to another IP 3 R antagonist caffeine [25,26] reduced the rate of Ca 2+ leakage.…”

Section: Introductionmentioning

confidence: 99%

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Ca2+-induced Ca2+ release by activation of inositol 1,4,5-trisphosphate receptors in primary pancreatic β-cells

2004

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The effect of sarcoendoplasmic reticulum Ca 2+ -ATPase (SERCA) inhibition on the The results indicate that leakage of Ca 2+ from the endoplasmic reticulum after SERCA inhibition is feedback-accelerated by Ca 2+ -induced Ca 2+ release (CICR). In primary pancreatic -cells this CICR is due to activation of inositol 1,4,5-trisphosphate receptors.CICR by ryanodine receptor activation may be restricted to clonal -cells.

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“…In both steady-state and luminal potential models, continuous activation of InsP 3 receptor channels by a constant concentration of InsP 3 [36] and/or openings of other 'leak' channels [37,38] are required for self-sustained oscillation. It may also be argued that such constant openings of Ca 2+ releasing channels are not enough for optimal Ca 2+ release.…”

Section: Ca 2+ Oscillation By 'Quantal' Ca 2+ Releasementioning

confidence: 99%

‘Quantal’ Ca²⁺ release reassessed – a clue to oscillation and synchronization

Yamashita

2006

FEBS Letters

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Ca 2+ release from intracellular Ca 2+ stores, a pivotal event in Ca 2+ signaling, is a 'quantal' process; it terminates after a rapid release of a fraction of stored Ca 2+ . To explain the 'quantal' nature, 'all-or-none' model and 'steady-state' model were proposed. This article shortly reviews these hypotheses and considers a recently proposed mechanism, 'luminal potential ' model, in The release of Ca 2+ from intracellular Ca 2+ stores shows complex kinetic behavior. By examining the kinetics of hormone-mediated 45 Ca 2+ efflux from pre-loaded stores, Muallem et al. [1] found that the Ca 2+ release is a 'quantal' rather than a continuous process; it consists of a rapid release of a fraction of stored Ca 2+ followed by no or a much slower efflux of Ca 2+ . This transient and partial release behavior has been termed 'quantal' Ca 2+ release [1].The 'quantal' release of Ca 2+ requires a mechanism for the attenuation of Ca 2+ efflux, such as inactivation of inositol 1,4,5-trisphosphate (InsP 3 ) receptor channels [2]. However, many studies have provided evidence for the lack of inactivation or desensitization of InsP 3 receptor channels [3][4][5][6][7][8][9]. Alternatively, the efflux of Ca 2+ may be compensated for by reuptake of Ca 2+ after a rapid release of Ca 2+ , as the activity of store Ca 2+ pumps is accelerated by a decrease in the concentration of Ca 2+ in the lumen of the Ca 2+ store [10]. However, this explanation was also unlikely because the transient Ca 2+ release occurs in the absence of Ca 2+ reuptake [3,4,8,9,[11][12][13].Another feature of 'quantal' Ca 2+ release is that the amount of Ca 2+ released depends on the dose of agonist or InsP 3 [1,3,4,6,8,9], or caffeine for ryanodine-sensitive Ca 2+ stores [14,15]. Meyer and Stryer [3] suggested that such dose dependent Ca 2+ release acts as an 'increment detector' in response to stepwise increases in stimulus intensity. To explain the kinetics and the dose dependence of 'quantal' Ca 2+ release, the following two hypotheses were proposed. 'All-or-none' model versus 'steady-state' modelMuallem et al.[1] first postulated that Ca 2+ ions are released from Ca 2+ stores in an all-or-none fashion ('all-or-none' model). Then Irvine [16] proposed another model, in which the sensitivity of InsP 3 receptor to InsP 3 is regulated by the luminal Ca 2+ concentration ('steady-state' model). Since these two models were proposed, numerous studies attempted to support or deny either of the two hypotheses. Missiaen et al.[17] and Bootman [18] extensively reviewed and discussed these hypotheses. The following is a short review of the two models including recent studies. All-or-none modelMuallem et al.[1] have supposed that intracellular Ca 2+ stores are compartmentalized and a submaximal dose of agonist or InsP 3 discharges all the Ca 2+ content in a fraction of the compartmentalized Ca 2+ stores. It is also assumed that the compartments of Ca 2+ store differ in the sensitivity to InsP 3 . According to this model, all the stored Ca 2+ ions are released fro...

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Basal and Physiological Ca2+ Leak from the Endoplasmic Reticulum of Pancreatic Acinar Cells

Cited by 116 publications

References 45 publications

The Permeability of the Endoplasmic Reticulum Is Dynamically Coupled to Protein Synthesis

The Permeability of the Endoplasmic Reticulum Is Dynamically Coupled to Protein Synthesis

Ca2+-induced Ca2+ release by activation of inositol 1,4,5-trisphosphate receptors in primary pancreatic β-cells

‘Quantal’ Ca²⁺ release reassessed – a clue to oscillation and synchronization

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Basal and Physiological Ca2+ Leak from the Endoplasmic Reticulum of Pancreatic Acinar Cells

Cited by 116 publications

References 45 publications

The Permeability of the Endoplasmic Reticulum Is Dynamically Coupled to Protein Synthesis

The Permeability of the Endoplasmic Reticulum Is Dynamically Coupled to Protein Synthesis

Ca2+-induced Ca2+ release by activation of inositol 1,4,5-trisphosphate receptors in primary pancreatic β-cells

‘Quantal’ Ca2+ release reassessed – a clue to oscillation and synchronization

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‘Quantal’ Ca²⁺ release reassessed – a clue to oscillation and synchronization