Abstract
Purkinje fibers of the sheep heart were exposed to (a) 0.1 mm dihydro-ouabain (DHO), followed by (b) 0.1 mm DHO in Na-free solution or to (c) 1 mm dinitrophenol (DNP). The degree of electrical decoupling was characterized in terms of the inside longitudinal resistance ri as measured with a 3-microelectrode voltage-clamp technique. Procedure a increased ri by a factor of 3.7±1.1 (mean±sd), b by a factor of 9.8±2.2, whereas in c incomplete voltage control indicated nearly complete uncoupling. Intracellular calcium activity (aCai) was monitored with a microelectrode system. At control conditions aCai was below 0.1 μm. The procedures listed above increased aCai to (a) 4±1.5 μm, (b) 8±2 μm, and (c) 36±12 μm. The increase of aCai was in good correlation with the changes in core resistance. Effects on nexus ultrastructure, investigated with freeze-fracture techniques, are shown in histograms. At control conditions, the particle diameter distributed around a single peak (8.3±0.5 nm). Procedures b and c induced a second population at 10.8 nm; increased decoupling reduced the control population in favor of the 10.8 nm population. Decoupling enlarged the width of the nexus gap by a factor of 1.6; again, the control population decreased in favor of a new population. In the decoupled state the height of the particle was smaller. Pits on the E-face displayed a more regular array and a nearly unchanged center-to-center spacing. Separation into several peaks was not possible due to scatter of the data. We interpret the findings to mean that elevated aCai induces a conformational change of the nexus subunits which corresponds to a transition from an open to a closed state. The conformational change can be formally described by a particle contraction which disrupts the continuity with the particle of the adjacent membrane. Purkinje fibers exposed to DNP for 1 hr showed thinned (7.7±0.5 mm) and elongated particles. We suggest that this is a secondary event and not a precursor of functional uncoupling.
| Original language | English |
|---|---|
| Pages (from-to) | 63-75 |
| Number of pages | 13 |
| Journal | The Journal of Membrane Biology |
| Volume | 53 |
| Issue number | 1 |
| DOIs | |
| State | Published - Feb 1 1980 |
| Externally published | Yes |
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Keywords
- freeze fracture EM
- heart
- intracellular calcium
- Nexus
- uncoupling
ASJC Scopus subject areas
- Physiology
- Cell Biology
- Biophysics
Cite this
Decoupling of heart muscle cells : Correlation with increased cytoplasmic calcium activity and with changes of nexus ultrastructure. / Dahl, Gerhard; Isenberg, Gerrit.
In: The Journal of Membrane Biology, Vol. 53, No. 1, 01.02.1980, p. 63-75.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Decoupling of heart muscle cells
T2 - Correlation with increased cytoplasmic calcium activity and with changes of nexus ultrastructure
AU - Dahl, Gerhard
AU - Isenberg, Gerrit
PY - 1980/2/1
Y1 - 1980/2/1
N2 - Purkinje fibers of the sheep heart were exposed to (a) 0.1 mm dihydro-ouabain (DHO), followed by (b) 0.1 mm DHO in Na-free solution or to (c) 1 mm dinitrophenol (DNP). The degree of electrical decoupling was characterized in terms of the inside longitudinal resistance ri as measured with a 3-microelectrode voltage-clamp technique. Procedure a increased ri by a factor of 3.7±1.1 (mean±sd), b by a factor of 9.8±2.2, whereas in c incomplete voltage control indicated nearly complete uncoupling. Intracellular calcium activity (aCai) was monitored with a microelectrode system. At control conditions aCai was below 0.1 μm. The procedures listed above increased aCai to (a) 4±1.5 μm, (b) 8±2 μm, and (c) 36±12 μm. The increase of aCai was in good correlation with the changes in core resistance. Effects on nexus ultrastructure, investigated with freeze-fracture techniques, are shown in histograms. At control conditions, the particle diameter distributed around a single peak (8.3±0.5 nm). Procedures b and c induced a second population at 10.8 nm; increased decoupling reduced the control population in favor of the 10.8 nm population. Decoupling enlarged the width of the nexus gap by a factor of 1.6; again, the control population decreased in favor of a new population. In the decoupled state the height of the particle was smaller. Pits on the E-face displayed a more regular array and a nearly unchanged center-to-center spacing. Separation into several peaks was not possible due to scatter of the data. We interpret the findings to mean that elevated aCai induces a conformational change of the nexus subunits which corresponds to a transition from an open to a closed state. The conformational change can be formally described by a particle contraction which disrupts the continuity with the particle of the adjacent membrane. Purkinje fibers exposed to DNP for 1 hr showed thinned (7.7±0.5 mm) and elongated particles. We suggest that this is a secondary event and not a precursor of functional uncoupling.
AB - Purkinje fibers of the sheep heart were exposed to (a) 0.1 mm dihydro-ouabain (DHO), followed by (b) 0.1 mm DHO in Na-free solution or to (c) 1 mm dinitrophenol (DNP). The degree of electrical decoupling was characterized in terms of the inside longitudinal resistance ri as measured with a 3-microelectrode voltage-clamp technique. Procedure a increased ri by a factor of 3.7±1.1 (mean±sd), b by a factor of 9.8±2.2, whereas in c incomplete voltage control indicated nearly complete uncoupling. Intracellular calcium activity (aCai) was monitored with a microelectrode system. At control conditions aCai was below 0.1 μm. The procedures listed above increased aCai to (a) 4±1.5 μm, (b) 8±2 μm, and (c) 36±12 μm. The increase of aCai was in good correlation with the changes in core resistance. Effects on nexus ultrastructure, investigated with freeze-fracture techniques, are shown in histograms. At control conditions, the particle diameter distributed around a single peak (8.3±0.5 nm). Procedures b and c induced a second population at 10.8 nm; increased decoupling reduced the control population in favor of the 10.8 nm population. Decoupling enlarged the width of the nexus gap by a factor of 1.6; again, the control population decreased in favor of a new population. In the decoupled state the height of the particle was smaller. Pits on the E-face displayed a more regular array and a nearly unchanged center-to-center spacing. Separation into several peaks was not possible due to scatter of the data. We interpret the findings to mean that elevated aCai induces a conformational change of the nexus subunits which corresponds to a transition from an open to a closed state. The conformational change can be formally described by a particle contraction which disrupts the continuity with the particle of the adjacent membrane. Purkinje fibers exposed to DNP for 1 hr showed thinned (7.7±0.5 mm) and elongated particles. We suggest that this is a secondary event and not a precursor of functional uncoupling.
KW - freeze fracture EM
KW - heart
KW - intracellular calcium
KW - Nexus
KW - uncoupling
UR - http://www.scopus.com/inward/record.url?scp=0018870828&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0018870828&partnerID=8YFLogxK
U2 - 10.1007/BF01871173
DO - 10.1007/BF01871173
M3 - Article
VL - 53
SP - 63
EP - 75
JO - Journal of Membrane Biology
JF - Journal of Membrane Biology
SN - 0022-2631
IS - 1
ER -