Quantitative assessment of the SR Ca2+ leak-load relationship. Export

@article{citeulike:1154869, abstract = {Increased diastolic SR Ca2+ 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 Ca2+ leak in intact, isolated ventricular myocytes. After stimulation, myocytes were exposed to 0 Na+, 0 Ca2+ solution +/-1 mmol/L tetracaine (to block resting leak). Total cell [Ca2+] does not change under these conditions with Na+-Ca2+ exchange inhibited. Resting [Ca2+]i declined 25\% after tetracaine addition (126+/-6 versus 94+/-6 nmol/L; P<0.05). At the same time, SR [Ca2+] ([Ca2+](SRT)) increased 20\% (93+/-8 versus 108+/-6 micromol/L). From this Ca2+ 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 Ca2+ effluxes is counterbalanced by unidirectional forward Ca2+ pump flux. J(leak) also increased nonlinearly with [Ca2+](SRT) with a steeper increase at higher load. We conclude that J(leak) is 4 to 15 micromol/L cytosol per second at physiological [Ca2+](SRT). The data suggest that the leak is steeply [Ca2+](SRT)-dependent, perhaps because of increased [Ca2+]i sensitivity of the ryanodine receptor at higher [Ca2+](SRT). Key factors that determine [Ca2+](SRT) in intact ventricular myocytes include (1) the thermodynamically limited Ca2+ gradient that the SR can develop (which depends on forward flux and backflux through the SR Ca2+ ATPase) and (2) diastolic SR Ca2+ leak (ryanodine receptor mediated).}, address = {Department of Physiology, Loyola University Chicago, Maywood, IL 60153, USA. tshanno@lumc.edu}, author = {Shannon, T. R. and Ginsburg, K. S. and Bers, D. M.}, citeulike-article-id = {1154869}, citeulike-linkout-0 = {http://dx.doi.org/10.1161/01.RES.0000036914.12686.28}, citeulike-linkout-1 = {http://circres.ahajournals.org/cgi/content/abstract/91/7/594}, citeulike-linkout-2 = {http://view.ncbi.nlm.nih.gov/pubmed/12364387}, citeulike-linkout-3 = {http://www.hubmed.org/display.cgi?uids=12364387}, day = {4}, doi = {10.1161/01.RES.0000036914.12686.28}, issn = {1524-4571}, journal = {Circ Res}, keywords = {backflux, heart-failure, leak-load-relation, ryr-regulation, sr-fluxes, sr-leak, sr-load, tetracaine, total-sr-ca, ventricular-myocytes}, month = {October}, number = {7}, pages = {594--600}, posted-at = {2008-07-07 22:47:41}, priority = {5}, title = {Quantitative assessment of the SR Ca2+ leak-load relationship.}, url = {http://dx.doi.org/10.1161/01.RES.0000036914.12686.28}, volume = {91}, year = {2002} }

TY - JOUR ID - citeulike:1154869 L3 - citeulike-article-id:1154869 N2 - Increased diastolic SR Ca2+ 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 Ca2+ leak in intact, isolated ventricular myocytes. After stimulation, myocytes were exposed to 0 Na+, 0 Ca2+ solution +/-1 mmol/L tetracaine (to block resting leak). Total cell [Ca2+] does not change under these conditions with Na+-Ca2+ exchange inhibited. Resting [Ca2+]i declined 25% after tetracaine addition (126+/-6 versus 94+/-6 nmol/L; P<0.05). At the same time, SR [Ca2+] ([Ca2+](SRT)) increased 20% (93+/-8 versus 108+/-6 micromol/L). From this Ca2+ 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 Ca2+ effluxes is counterbalanced by unidirectional forward Ca2+ pump flux. J(leak) also increased nonlinearly with [Ca2+](SRT) with a steeper increase at higher load. We conclude that J(leak) is 4 to 15 micromol/L cytosol per second at physiological [Ca2+](SRT). The data suggest that the leak is steeply [Ca2+](SRT)-dependent, perhaps because of increased [Ca2+]i sensitivity of the ryanodine receptor at higher [Ca2+](SRT). Key factors that determine [Ca2+](SRT) in intact ventricular myocytes include (1) the thermodynamically limited Ca2+ gradient that the SR can develop (which depends on forward flux and backflux through the SR Ca2+ ATPase) and (2) diastolic SR Ca2+ leak (ryanodine receptor mediated). IS - 7 JF - Circ Res SN - 1524-4571 AD - Department of Physiology, Loyola University Chicago, Maywood, IL 60153, USA. tshanno@lumc.edu EP - 600 TI - Quantitative assessment of the SR Ca2+ leak-load relationship. VL - 91 SP - 594 KW - backflux KW - heart-failure KW - leak-load-relation KW - ryr-regulation KW - sr-fluxes KW - sr-leak KW - sr-load KW - tetracaine KW - total-sr-ca KW - ventricular-myocytes AU - Shannon, TR AU - Ginsburg, KS AU - Bers, DM PY - 2002/10/04/ UR - http://dx.doi.org/10.1161/01.RES.0000036914.12686.28 ER -