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 micromol/L). From this Ca$^2+$
shift, we calculate J(leak) to be 12 micromol/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(leak) also increased nonlinearly with Ca$^2+$(SRT) with
a steeper increase at higher load. We conclude that J(leak) is 4
to 15 micromol/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).
%0 Journal Article
%1 Shan_2002_594
%A Shannon, Thomas R
%A Ginsburg, Kenneth S
%A Bers, Donald M
%D 2002
%J Circ. Res.
%K 12364387 Animals, Calcium Calcium, Cardiovascular, Cells, Channels, Congestive, Contraction, Cultured, Diastole, Failure, Gov't, Heart Heart, Ion Kinetics, Models, Myocardial Myocardium, Non-U.S. P.H.S., Rabbits, Research Reticulum, Sarcoplasmic Support, Tetracaine, Transport, U.S.
%N 7
%P 594--600
%T Quantitative assessment of the SR Ca$^2+$ leak-load relationship.
%U http://circres.ahajournals.org/cgi/content/full/91/7/594
%V 91
%X 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 micromol/L). From this Ca$^2+$
shift, we calculate J(leak) to be 12 micromol/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(leak) also increased nonlinearly with Ca$^2+$(SRT) with
a steeper increase at higher load. We conclude that J(leak) is 4
to 15 micromol/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).
@article{Shan_2002_594,
abstract = {Increased diastolic SR {C}a$^{2+}$ 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 {C}a$^{2+}$ leak in intact, isolated
ventricular myocytes. After stimulation, myocytes were exposed to
0 {N}a$^{+}$, 0 {C}a$^{2+}$ solution +/-1 mmol/L tetracaine (to block
resting leak). Total cell [{C}a$^{2+}$] does not change under these
conditions with {N}a$^{+}$-{C}a$^{2+}$ exchange inhibited. Resting
[{C}a$^{2+}$]i declined 25\% after tetracaine addition (126+/-6 versus
94+/-6 nmol/L; P<0.05). At the same time, SR [{C}a$^{2+}$] ([{C}a$^{2+}$]({SRT}))
increased 20\% (93+/-8 versus 108+/-6 micromol/L). From this {C}a$^{2+}$
shift, we calculate J(leak) to be 12 micromol/L per second or 30\%
of the SR diastolic efflux. The remaining 70\% is SR pump unidirectional
reverse flux (backflux). The sum of these {C}a$^{2+}$ effluxes is
counterbalanced by unidirectional forward {C}a$^{2+}$ pump flux.
J(leak) also increased nonlinearly with [{C}a$^{2+}$]({SRT}) with
a steeper increase at higher load. We conclude that J(leak) is 4
to 15 micromol/L cytosol per second at physiological [{C}a$^{2+}$]({SRT}).
The data suggest that the leak is steeply [{C}a$^{2+}$]({SRT})-dependent,
perhaps because of increased [{C}a$^{2+}$]i sensitivity of the ryanodine
receptor at higher [{C}a$^{2+}$]({SRT}). Key factors that determine
[{C}a$^{2+}$]({SRT}) in intact ventricular myocytes include (1) the
thermodynamically limited {C}a$^{2+}$ gradient that the SR can develop
(which depends on forward flux and backflux through the SR {C}a$^{2+}$
ATPase) and (2) diastolic SR {C}a$^{2+}$ leak (ryanodine receptor
mediated).},
added-at = {2009-06-03T11:20:58.000+0200},
author = {Shannon, Thomas R and Ginsburg, Kenneth S and Bers, Donald M},
biburl = {https://www.bibsonomy.org/bibtex/28e6874862f9eb087e125d4e4532937e0/hake},
description = {The whole bibliography file I use.},
file = {Shan_2002_594.pdf:Shan_2002_594.pdf:PDF},
interhash = {65b72dfe660320b07c24d4e5aebb65d0},
intrahash = {8e6874862f9eb087e125d4e4532937e0},
journal = {Circ. Res.},
key = 111,
keywords = {12364387 Animals, Calcium Calcium, Cardiovascular, Cells, Channels, Congestive, Contraction, Cultured, Diastole, Failure, Gov't, Heart Heart, Ion Kinetics, Models, Myocardial Myocardium, Non-U.S. P.H.S., Rabbits, Research Reticulum, Sarcoplasmic Support, Tetracaine, Transport, U.S.},
month = Oct,
number = 7,
pages = {594--600},
pmid = {12364387},
timestamp = {2009-06-03T11:21:29.000+0200},
title = {Quantitative assessment of the SR {C}a$^{2+}$ leak-load relationship.},
url = {http://circres.ahajournals.org/cgi/content/full/91/7/594},
volume = 91,
year = 2002
}