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Thapsigargin, but not ryanodine, suppresses high [K+]e-induced cytosolic Ca2+ transients in the absence, but not in the presence, of extracellular Ca2+.

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posted on 09.02.2016, 09:22 by Hong-Li Sun, Wen-Chin Tsai, Bai-Yan Li, Wen Tao, Peng-Sheng Chen, Michael Rubart

A: Time course of cytosolic ΔF/F0 during 30-s exposures to 80 mM [K+]e in 2 mM [Ca2+]e (left panel) and in the absence of external Ca2+. To deplete internal Ca2+ stores, cells were continuously incubated with thapsigargin (1 μM) starting 20 min before the first exposure to elevated [K+]e. B: Percentage of cells exhibiting [Ca2+]i transients both in 2 mM and 0 mM [Ca2+]e; * P < 0.001 versus control by Fisher Exact test (60 cells for control and 19 cells for thapsigargin). C: Time course of changes in cytosolic ΔF/F0 elicited by consecutive 30-s exposures to 80 mM [K+]e in normal [Ca2+]e (upper panel) and in Ca2+-free bath solution (with 200 μM EGTA added). The cell was continuously incubated with ryanodine (20 μM) starting 20 min before the first [K+]e challenge. D: Percentage of cells exhibiting [Ca2+]i transients both in 2 mM and 0 mM [Ca2+]e; P = non-significant versus control by Fisher’s Exact test (60 cells for control and 14 cells for ryanodine). E: Ryanodine depletes caffeine-sensitive internal Ca2+ stores in postganglionic sympathetic neurons. Time course of changes in cytosolic ΔF/F0 in response to a 30-s exposure to 80 mM [K+]e followed by a 30-s exposure to caffeine (upper panel). Preincubation with 20 μM ryanodine abrogated the caffeine-, but not the high [K+]e-, induced cytosolic Ca2+ transient (lower panel). Caffeine responses in the presence and absence of ryanodine were monitored in two different cells.

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