Premium
Na + –Ca 2+ exchange and its implications for calcium homeostasis in primary cultured rat brain microvascular endothelial cells
Author(s) -
Dömötör Eszter,
Abbott N. Joan,
AdamVizi Vera
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.147ad.x
Subject(s) - neurochemical , medicine , chemistry
1 The role of Na + –Ca 2+ exchange in the regulation of the cytosolic free Ca 2+ concentration ([Ca 2+ ] i ) was studied in primary cultured rat brain capillary endothelial cells. [Ca 2+ ] i was measured by digital fluorescence imaging in cells loaded with fura‐2. 2 ATP (100 μ m ) applied for a short period of time (6 s) caused a rise in [Ca 2+ ] i from 127 ± 3 ( n = 290 ) to 797 ± 25 n m , which then declined to the resting level, with a t ½ time required for [Ca 2+ ] i to decline to half of peak [Ca 2+ ] i ) of 5.4 ± 0.09 s. This effect was independent of external Ca 2+ and could be abolished by previously discharging the Ca 2+ pool of the endoplasmic reticulum with thapsigargin (1 μ m ). 3 Application of thapsigargin (1 μ m ) or cyclopiazonic acid (10 μ m ) to inhibit the Ca 2+ ‐ATPase of the endoplasmic reticulum 6 s prior to ATP application did not influence the peak [Ca 2+ ] i but greatly reduced the rate of decline of [Ca 2+ ] i , with t ½ values of 15 ± 1.6 and 23 ± 3 s, respectively. 4 In the absence of external Na + (Na + replaced by Li + or N‐ methylglucamine) the basal [Ca 2+ ] i was slightly elevated (152 ± 6 n m ) and the restoration of [Ca 2+ ] i after the ATP stimulation was significantly slower ( t ½ , 7.3 ± 0.46 s in Li + medium, 8.12 ± 0.4 s in N‐ methylglucamine medium). 5 The external Na + ‐dependent component of the [Ca 2+ ] i sequestration was also demonstrated in cells stimulated by ATP subsequent to addition of cyclopiazonic acid; in a Na + ‐free medium [Ca 2+ ] i remained at the peak level in 88% of the cells after stimulation with ATP. 6 Addition of monensin (10 μ m ) in the presence of external Na + increased the resting [Ca 2+ ] i to 222 ± 9 n m over ∼1 min and subsequent removal of extracellular sodium resulted in a further increase in [Ca 2+ ] i to a peak of 328 ± 11 n m , which was entirely dependent on external Ca 2+ . 7 These findings indicate that a functional Na + –Ca 2+ exchanger is present at the blood‐brain barrier, which plays a significant role in shaping the stimulation‐evoked [Ca 2+ ] i signal and is able to work in reverse mode under pharmacological conditions.