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Concerted vs. sequential. Two activation patterns of vast arrays of intracellular Ca2+ channels in muscle.

Zhou J, Brum G, González A, Launikonis BS, Stern MD, Ríos E - J. Gen. Physiol. (2005)

Bottom Line: When sulfate was combined with a reduced cytosolic [Ca(2+)] (50 nM) these sparks coexisted (and interfered) with a sequential progression of channel opening, probably mediated by Ca(2+)-induced Ca(2+) release (CICR).Sequential propagation, observed only in frogs, may require parajunctional channels, of RyR isoform beta, which are absent in the rat.Concerted opening instead appears to be a property of RyR alpha in the amphibian and the homologous isoform 1 in the mammal.

View Article: PubMed Central - PubMed

Affiliation: Section of Cellular Signaling, Rush University, Chicago, IL 60612, USA.

ABSTRACT
To signal cell responses, Ca(2+) is released from storage through intracellular Ca(2+) channels. Unlike most plasmalemmal channels, these are clustered in quasi-crystalline arrays, which should endow them with unique properties. Two distinct patterns of local activation of Ca(2+) release were revealed in images of Ca(2+) sparks in permeabilized cells of amphibian muscle. In the presence of sulfate, an anion that enters the SR and precipitates Ca(2+), sparks became wider than in the conventional, glutamate-based solution. Some of these were "protoplatykurtic" (had a flat top from early on), suggesting an extensive array of channels that activate simultaneously. Under these conditions the rate of production of signal mass was roughly constant during the rise time of the spark and could be as high as 5 microm(3) ms(-1), consistent with a release current >50 pA since the beginning of the event. This pattern, called "concerted activation," was observed also in rat muscle fibers. When sulfate was combined with a reduced cytosolic [Ca(2+)] (50 nM) these sparks coexisted (and interfered) with a sequential progression of channel opening, probably mediated by Ca(2+)-induced Ca(2+) release (CICR). Sequential propagation, observed only in frogs, may require parajunctional channels, of RyR isoform beta, which are absent in the rat. Concerted opening instead appears to be a property of RyR alpha in the amphibian and the homologous isoform 1 in the mammal.

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Hypothetical mechanisms of two activation patterns in frog fibers. Triads are drawn progressively separated and stripped of components from left to right. α channels, in blue, are grouped in couplons that face the junctional gap. They undergo concerted activation, pictured as a Ca2+-mediated interaction that propagates very rapidly in the narrow gap, then stops at the edges of the couplon. Sequential activation is attributed to β channels (green), facing the wide parajunctional space. Ca2+-mediated activation there should propagate more slowly, but freely, without defined structural bounds. “Mixed” events are not excluded in this view.
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fig6: Hypothetical mechanisms of two activation patterns in frog fibers. Triads are drawn progressively separated and stripped of components from left to right. α channels, in blue, are grouped in couplons that face the junctional gap. They undergo concerted activation, pictured as a Ca2+-mediated interaction that propagates very rapidly in the narrow gap, then stops at the edges of the couplon. Sequential activation is attributed to β channels (green), facing the wide parajunctional space. Ca2+-mediated activation there should propagate more slowly, but freely, without defined structural bounds. “Mixed” events are not excluded in this view.

Mentions: A molecular underpinning for dual mechanisms is suggested by the absence of sequential events in the rat, where sulfate only alters event frequency (Zhou et al., 2003a). As sketched for frog muscle in Fig. 6, concerted events, virtually identical in both species, should originate at the junctional arrays of α or RyR1 isoforms. Sequential activation should instead require β channels, green in the diagram.


Concerted vs. sequential. Two activation patterns of vast arrays of intracellular Ca2+ channels in muscle.

Zhou J, Brum G, González A, Launikonis BS, Stern MD, Ríos E - J. Gen. Physiol. (2005)

Hypothetical mechanisms of two activation patterns in frog fibers. Triads are drawn progressively separated and stripped of components from left to right. α channels, in blue, are grouped in couplons that face the junctional gap. They undergo concerted activation, pictured as a Ca2+-mediated interaction that propagates very rapidly in the narrow gap, then stops at the edges of the couplon. Sequential activation is attributed to β channels (green), facing the wide parajunctional space. Ca2+-mediated activation there should propagate more slowly, but freely, without defined structural bounds. “Mixed” events are not excluded in this view.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2266625&req=5

fig6: Hypothetical mechanisms of two activation patterns in frog fibers. Triads are drawn progressively separated and stripped of components from left to right. α channels, in blue, are grouped in couplons that face the junctional gap. They undergo concerted activation, pictured as a Ca2+-mediated interaction that propagates very rapidly in the narrow gap, then stops at the edges of the couplon. Sequential activation is attributed to β channels (green), facing the wide parajunctional space. Ca2+-mediated activation there should propagate more slowly, but freely, without defined structural bounds. “Mixed” events are not excluded in this view.
Mentions: A molecular underpinning for dual mechanisms is suggested by the absence of sequential events in the rat, where sulfate only alters event frequency (Zhou et al., 2003a). As sketched for frog muscle in Fig. 6, concerted events, virtually identical in both species, should originate at the junctional arrays of α or RyR1 isoforms. Sequential activation should instead require β channels, green in the diagram.

Bottom Line: When sulfate was combined with a reduced cytosolic [Ca(2+)] (50 nM) these sparks coexisted (and interfered) with a sequential progression of channel opening, probably mediated by Ca(2+)-induced Ca(2+) release (CICR).Sequential propagation, observed only in frogs, may require parajunctional channels, of RyR isoform beta, which are absent in the rat.Concerted opening instead appears to be a property of RyR alpha in the amphibian and the homologous isoform 1 in the mammal.

View Article: PubMed Central - PubMed

Affiliation: Section of Cellular Signaling, Rush University, Chicago, IL 60612, USA.

ABSTRACT
To signal cell responses, Ca(2+) is released from storage through intracellular Ca(2+) channels. Unlike most plasmalemmal channels, these are clustered in quasi-crystalline arrays, which should endow them with unique properties. Two distinct patterns of local activation of Ca(2+) release were revealed in images of Ca(2+) sparks in permeabilized cells of amphibian muscle. In the presence of sulfate, an anion that enters the SR and precipitates Ca(2+), sparks became wider than in the conventional, glutamate-based solution. Some of these were "protoplatykurtic" (had a flat top from early on), suggesting an extensive array of channels that activate simultaneously. Under these conditions the rate of production of signal mass was roughly constant during the rise time of the spark and could be as high as 5 microm(3) ms(-1), consistent with a release current >50 pA since the beginning of the event. This pattern, called "concerted activation," was observed also in rat muscle fibers. When sulfate was combined with a reduced cytosolic [Ca(2+)] (50 nM) these sparks coexisted (and interfered) with a sequential progression of channel opening, probably mediated by Ca(2+)-induced Ca(2+) release (CICR). Sequential propagation, observed only in frogs, may require parajunctional channels, of RyR isoform beta, which are absent in the rat. Concerted opening instead appears to be a property of RyR alpha in the amphibian and the homologous isoform 1 in the mammal.

Show MeSH
Related in: MedlinePlus