Quantitative assessment of the SR Ca 2+ leak-load relationship

Thomas R. Shannon, Kenneth S Ginsburg, Donald M Bers

Research output: Contribution to journalArticle

201 Citations (Scopus)

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 languageEnglish (US)
Pages (from-to)594-600
Number of pages7
JournalCirculation Research
Volume91
Issue number7
DOIs
StatePublished - Oct 4 2002
Externally publishedYes

Fingerprint

Muscle Cells
Tetracaine
Ryanodine Receptor Calcium Release Channel
Sarcoplasmic Reticulum Calcium-Transporting ATPases
Cytosol
Heart Failure

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 journalArticle

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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).",
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