Assessment of sarcoplasmic reticulum Ca2+ depletion during spontaneous Ca2+ waves in isolated permeabilized rabbit ventricular cardiomyocytes. Export

@article{citeulike:5189752, abstract = {In this study, Ca2+ release due to spontaneous Ca2+ waves was measured both from inside the sarcoplasmic reticulum (SR) and from the cytosol of rabbit cardiomyocytes. These measurements utilized Fluo5N-AM for intra-SR Ca2+ from intact cells and Fluo5F in the cytosol of permeabilized cells. Restricted subcellular volumes were resolved with the use of laser-scanning confocal microscopy. Local Ca2+ signals during spontaneous Ca2+ release were compared with those induced by rapid caffeine application. The free cytoplasmic [Ca2+] increase during a Ca2+ wave was 98.1\% +/- 0.3\% of that observed during caffeine application. Conversion to total Ca2+ release suggested that Ca2+ release from a Ca2+ wave was not significantly different from that released during caffeine application (104\% +/- 6\%). In contrast, the maximum decrease in intra-SR Fluo-5N fluorescence during a Ca2+ wave was 82.5\% +/- 2.6\% of that observed during caffeine application. Assuming a maximum free [Ca2+] of 1.1 mM, this translates to a 96.2\% +/- 0.8\% change in intra-SR free [Ca2+] and a 91.7\% +/- 1.6\% depletion of the total Ca2+. This equates to a minimum intra-SR free Ca2+ of 46 +/- 7 microM during a Ca2+ wave. Reduction of RyR2 Ca2+ sensitivity by tetracaine (50 microM) reduced the spontaneous Ca2+ release frequency while increasing the Ca2+ wave amplitude. This did not significantly change the total depletion of the SR (94.5\% +/- 1.1\%). The calculated minimum [Ca2+] during these Ca2+ waves (87 +/- 19 microM) was significantly higher than control (p < 0.05). A computational model incorporating this level of Ca2+ depletion during a Ca2+ wave mimicked the transient and sustained effects of tetracaine on spontaneous Ca2+ release. In conclusion, spontaneous Ca2+ release results in substantial but not complete local Ca2+ depletion of the SR. Furthermore, measurements suggest that Ca2+ release terminates when luminal [Ca2+] reaches approximately 50 microM.}, author = {MacQuaide, N. and Dempster, J. and Smith, G. L.}, citeulike-article-id = {5189752}, citeulike-linkout-0 = {http://dx.doi.org/10.1016/j.bpj.2008.12.3944}, citeulike-linkout-1 = {http://view.ncbi.nlm.nih.gov/pubmed/19348757}, citeulike-linkout-2 = {http://www.hubmed.org/display.cgi?uids=19348757}, day = {8}, doi = {10.1016/j.bpj.2008.12.3944}, issn = {1542-0086}, journal = {Biophysical journal}, keywords = {calcium, cardiac, depletion, myocyte, rabbit, reticulum, sarcoplasmic, ventricle}, month = {April}, number = {7}, pages = {2744--2754}, posted-at = {2009-07-17 08:10:26}, priority = {2}, title = {Assessment of sarcoplasmic reticulum Ca2+ depletion during spontaneous Ca2+ waves in isolated permeabilized rabbit ventricular cardiomyocytes.}, url = {http://dx.doi.org/10.1016/j.bpj.2008.12.3944}, volume = {96}, year = {2009} }

TY - JOUR ID - citeulike:5189752 L3 - citeulike-article-id:5189752 N2 - In this study, Ca2+ release due to spontaneous Ca2+ waves was measured both from inside the sarcoplasmic reticulum (SR) and from the cytosol of rabbit cardiomyocytes. These measurements utilized Fluo5N-AM for intra-SR Ca2+ from intact cells and Fluo5F in the cytosol of permeabilized cells. Restricted subcellular volumes were resolved with the use of laser-scanning confocal microscopy. Local Ca2+ signals during spontaneous Ca2+ release were compared with those induced by rapid caffeine application. The free cytoplasmic [Ca2+] increase during a Ca2+ wave was 98.1% +/- 0.3% of that observed during caffeine application. Conversion to total Ca2+ release suggested that Ca2+ release from a Ca2+ wave was not significantly different from that released during caffeine application (104% +/- 6%). In contrast, the maximum decrease in intra-SR Fluo-5N fluorescence during a Ca2+ wave was 82.5% +/- 2.6% of that observed during caffeine application. Assuming a maximum free [Ca2+] of 1.1 mM, this translates to a 96.2% +/- 0.8% change in intra-SR free [Ca2+] and a 91.7% +/- 1.6% depletion of the total Ca2+. This equates to a minimum intra-SR free Ca2+ of 46 +/- 7 microM during a Ca2+ wave. Reduction of RyR2 Ca2+ sensitivity by tetracaine (50 microM) reduced the spontaneous Ca2+ release frequency while increasing the Ca2+ wave amplitude. This did not significantly change the total depletion of the SR (94.5% +/- 1.1%). The calculated minimum [Ca2+] during these Ca2+ waves (87 +/- 19 microM) was significantly higher than control (p < 0.05). A computational model incorporating this level of Ca2+ depletion during a Ca2+ wave mimicked the transient and sustained effects of tetracaine on spontaneous Ca2+ release. In conclusion, spontaneous Ca2+ release results in substantial but not complete local Ca2+ depletion of the SR. Furthermore, measurements suggest that Ca2+ release terminates when luminal [Ca2+] reaches approximately 50 microM. IS - 7 JF - Biophysical journal SN - 1542-0086 EP - 2754 TI - Assessment of sarcoplasmic reticulum Ca2+ depletion during spontaneous Ca2+ waves in isolated permeabilized rabbit ventricular cardiomyocytes. VL - 96 SP - 2744 KW - calcium KW - cardiac KW - depletion KW - myocyte KW - rabbit KW - reticulum KW - sarcoplasmic KW - ventricle AU - MacQuaide, N AU - Dempster, J AU - Smith, GL PY - 2009/04/08/ UR - http://dx.doi.org/10.1016/j.bpj.2008.12.3944 ER -