Abstract
Increased diastolic SR Ca 2+ leak (J leak) could depress contractility in heart failure, but there are conflicting reports regarding the J leak magnitude even in normal, intact myocytes. We have developed a novel approach to measure SR Ca 2+ leak in intact, isolated ventricular myocytes. After stimulation, myocytes were exposed to 0 Na +, 0 Ca 2+ solution ± 1 mmol/L tetracaine (to block resting leak). Total cell [Ca 2+] does not change under these conditions with Na +-Ca 2+ exchange inhibited. Resting [Ca 2+]i declined 25% after tetracaine addition (126±6 versus 94±6 nmol/L; P<0.05). At the same time, SR [Ca 2+] ([Ca 2+] SRT) increased 20% (93±8 versus 108±6 μmol/L). From this Ca 2+ shift, we calculate J leak to be 12 μmol/L per second or 30% of the SR diastolic efflux. The remaining 70% is SR pump unidirectional reverse flux (backflux). The sum of these Ca 2+ effluxes is counterbalanced by unidirectional forward Ca 2+ pump flux. J leakalso increased nonlinearly with [Ca 2+] SRT with a steeper increase at higher load. We conclude that J leak is 4 to 15 μmol/L cytosol per second at physiological [Ca 2+] SRT. The data suggest that the leak is steeply [Ca 2+] SRT-dependent, perhaps because of increased [Ca 2+] i sensitivity of the ryanodine receptor at higher [Ca 2+] SRT. Key factors that determine [Ca 2+] SRT in intact ventricular myocytes include (1) the thermodynamically limited Ca 2+ gradient that the SR can develop (which depends on forward flux and backflux through the SR Ca 2+ ATPase) and (2) diastolic SR Ca 2+ leak (ryanodine receptor mediated).
| Original language | English (US) |
|---|---|
| Pages (from-to) | 594-600 |
| Number of pages | 7 |
| Journal | Circulation Research |
| Volume | 91 |
| Issue number | 7 |
| DOIs | |
| State | Published - Oct 4 2002 |
| Externally published | Yes |
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Keywords
- Ca cycling
- Excitation-contraction coupling
- Membrane transport
- Ryanodine receptors
- Sarcoplasmic reticulum
ASJC Scopus subject areas
- Physiology
- Cardiology and Cardiovascular Medicine
Cite this
Quantitative assessment of the SR Ca 2+ leak-load relationship. / Shannon, Thomas R.; Ginsburg, Kenneth S; Bers, Donald M.
In: Circulation Research, Vol. 91, No. 7, 04.10.2002, p. 594-600.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Quantitative assessment of the SR Ca 2+ leak-load relationship
AU - Shannon, Thomas R.
AU - Ginsburg, Kenneth S
AU - Bers, Donald M
PY - 2002/10/4
Y1 - 2002/10/4
N2 - Increased diastolic SR Ca 2+ leak (J leak) could depress contractility in heart failure, but there are conflicting reports regarding the J leak magnitude even in normal, intact myocytes. We have developed a novel approach to measure SR Ca 2+ leak in intact, isolated ventricular myocytes. After stimulation, myocytes were exposed to 0 Na +, 0 Ca 2+ solution ± 1 mmol/L tetracaine (to block resting leak). Total cell [Ca 2+] does not change under these conditions with Na +-Ca 2+ exchange inhibited. Resting [Ca 2+]i declined 25% after tetracaine addition (126±6 versus 94±6 nmol/L; P<0.05). At the same time, SR [Ca 2+] ([Ca 2+] SRT) increased 20% (93±8 versus 108±6 μmol/L). From this Ca 2+ shift, we calculate J leak to be 12 μmol/L per second or 30% of the SR diastolic efflux. The remaining 70% is SR pump unidirectional reverse flux (backflux). The sum of these Ca 2+ effluxes is counterbalanced by unidirectional forward Ca 2+ pump flux. J leakalso increased nonlinearly with [Ca 2+] SRT with a steeper increase at higher load. We conclude that J leak is 4 to 15 μmol/L cytosol per second at physiological [Ca 2+] SRT. The data suggest that the leak is steeply [Ca 2+] SRT-dependent, perhaps because of increased [Ca 2+] i sensitivity of the ryanodine receptor at higher [Ca 2+] SRT. Key factors that determine [Ca 2+] SRT in intact ventricular myocytes include (1) the thermodynamically limited Ca 2+ gradient that the SR can develop (which depends on forward flux and backflux through the SR Ca 2+ ATPase) and (2) diastolic SR Ca 2+ leak (ryanodine receptor mediated).
AB - Increased diastolic SR Ca 2+ leak (J leak) could depress contractility in heart failure, but there are conflicting reports regarding the J leak magnitude even in normal, intact myocytes. We have developed a novel approach to measure SR Ca 2+ leak in intact, isolated ventricular myocytes. After stimulation, myocytes were exposed to 0 Na +, 0 Ca 2+ solution ± 1 mmol/L tetracaine (to block resting leak). Total cell [Ca 2+] does not change under these conditions with Na +-Ca 2+ exchange inhibited. Resting [Ca 2+]i declined 25% after tetracaine addition (126±6 versus 94±6 nmol/L; P<0.05). At the same time, SR [Ca 2+] ([Ca 2+] SRT) increased 20% (93±8 versus 108±6 μmol/L). From this Ca 2+ shift, we calculate J leak to be 12 μmol/L per second or 30% of the SR diastolic efflux. The remaining 70% is SR pump unidirectional reverse flux (backflux). The sum of these Ca 2+ effluxes is counterbalanced by unidirectional forward Ca 2+ pump flux. J leakalso increased nonlinearly with [Ca 2+] SRT with a steeper increase at higher load. We conclude that J leak is 4 to 15 μmol/L cytosol per second at physiological [Ca 2+] SRT. The data suggest that the leak is steeply [Ca 2+] SRT-dependent, perhaps because of increased [Ca 2+] i sensitivity of the ryanodine receptor at higher [Ca 2+] SRT. Key factors that determine [Ca 2+] SRT in intact ventricular myocytes include (1) the thermodynamically limited Ca 2+ gradient that the SR can develop (which depends on forward flux and backflux through the SR Ca 2+ ATPase) and (2) diastolic SR Ca 2+ leak (ryanodine receptor mediated).
KW - Ca cycling
KW - Excitation-contraction coupling
KW - Membrane transport
KW - Ryanodine receptors
KW - Sarcoplasmic reticulum
UR - http://www.scopus.com/inward/record.url?scp=0037019969&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0037019969&partnerID=8YFLogxK
U2 - 10.1161/01.RES.0000036914.12686.28
DO - 10.1161/01.RES.0000036914.12686.28
M3 - Article
C2 - 12364387
AN - SCOPUS:0037019969
VL - 91
SP - 594
EP - 600
JO - Circulation Research
JF - Circulation Research
SN - 0009-7330
IS - 7
ER -