%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 }