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Sodium‐calcium exchange in cultured bovine pulmonary artery endothelial cells.
Author(s) -
Sage S O,
van Breemen C,
Cannell M B
Publication year - 1991
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 - 10.1113/jphysiol.1991.sp018725
Subject(s) - ouabain , extracellular , sodium , monensin , calcium , depolarization , chemistry , biophysics , fura 2 , intracellular , medicine , biochemistry , biology , enzyme , organic chemistry , cytosol
1. Intracellular free calcium ([Ca2+]i) was measured in cultured bovine pulmonary artery endothelial cell monolayers loaded with the fluorescent calcium indicator Fura‐2. 2. Resting [Ca2+]i was 112 +/‐ 10 nM. Application of ouabain (20 microM) was without effect on [Ca2+]i for periods of up to 1 h. Monensin (10 microM) resting [Ca2+]i to 145 +/‐ 32 nM over approximately 2 min. In the presence of ouabain (20 microM), 10 microM‐monensin increased [Ca2+]i to 146 +/‐ 15 nM. 3. Removal of extracellular sodium was without effect in resting cells or cells exposed to ouabain alone. However, in the presence of monensin, replacement of extracellular Na+ with Li+ resulted in a prompt increase in [Ca2+]i to a peak of 280 +/‐ 37 nM, which then returned towards resting levels. When Na+ was removed in the presence of both ouabain and monensin, [Ca2+]i reached a peak of 585 +/‐ 53 nM. 4. When extracellular Na+ was replaced with K+, to achieve simultaneous Na+ removal and depolarization, [Ca2+]i reached a peak of 568 +/‐ 63 nM, compared with a peak of 462 +/‐ 38 nM when Li+ was used as a Na+ substitute in paired experiments. The transient increase in [Ca2+]i evoked by sodium removal peaked earlier when K+ was used as the sodium substitute, showing that depolarization increased the rate of calcium influx into the cell when sodium was removed from the bathing medium. 5. Removal of extracellular K+ had no effect on the low‐Na(+)‐evoked increase in [Ca2+]i. 6. Returning extracellular Na+ during the increase in [Ca2+]i resulting from Na+ removal increased the rate of return of [Ca2+]i towards basal levels. In the absence of Na+, [Ca2+]i took 41 +/‐ 5 s to decline from 400 to 200 nM, and this was reduced to 26 +/‐ 6 s (n = 4, S.E.M.) when Na+ was returned to the bathing solution. 7. These results indicate endothelial cells possess a voltage‐dependent Na(+) ‐Ca2+ exchange mechanism in the surface membrane. However, this mechanism does not appear to be of primary importance in the maintenance of resting [Ca2+]i since cells were able to restore a low [Ca2+]i in the absence of extracellular Na+. The evidence for the existence of a Na(+) ‐Ca2+ exchanger in the surface membrane of endothelial cells and the possibility that this mechanism may contribute to calcium entry and/or extrusion during agonist‐evoked responses is discussed.