Affiliation:
1. From the Laboratory of Cardiovascular Science (S.C., H.A.S., E.G.L., M.C.C.), Gerontology Research Center, National Institute on Aging, National Institutes of Health, and the Department of Medicine (M.C.C., R.C.Z.), Division of Cardiology, Johns Hopkins University, Baltimore, MD.
Abstract
Abstract
Intracellular Ca
2+
pools contribute to changes in cytosolic [Ca
2+
] ([Ca
2+
]
i
), which play an important role in endothelial cell signaling. Recently, endothelial ryanodine-sensitive Ca
2+
stores were shown to regulate agonist-sensitive intracellular Ca
2+
pools. Since caffeine binds the ryanodine Ca
2+
release channel on the endoplasmic reticulum in a variety of cell types, we examined the effect of caffeine on [Ca
2+
]
i
in human aortic endothelial cell monolayers loaded with the fluorescent probe indo 1. Under baseline conditions, 10 mmol/L caffeine induced a small increase in [Ca
2+
]
i
from 86±10 to 115±17 nmol/L (mean±SEM); this effect was similar to that of 5 μmol/L ryanodine and was unaffected by buffer Ca
2+
removal. After depletion of an intracellular Ca
2+
store by the irreversible endoplasmic reticulum Ca
2+
-ATPase inhibitor thapsigargin (1 μmol/L), ryanodine did not affect [Ca
2+
]
i
. In contrast, caffeine induced a large rapid increase in [Ca
2+
]
i
(176±19 to 338±35 nmol/L,
P
<.001) after thapsigargin exposure; this effect of caffeine was only observed when extracellular Ca
2+
was present. A similar increase in [Ca
2+
]
i
was induced by caffeine after depletion of ryanodine- and histamine-sensitive Ca
2+
stores or after pretreatment with the endoplasmic reticulum Ca
2+
-ATPase inhibitor cyclopiazonic acid (10 μmol/L). Thus, under baseline conditions the effect of caffeine on [Ca
2+
]
i
is similar to that of ryanodine and appears to be due to the release of an intracellular store. However, after depletion of an endoplasmic reticulum Ca
2+
store, caffeine, but not ryanodine, stimulates Ca
2+
influx, resulting in a large increase in [Ca
2+
]
i
. The data suggest that caffeine-induced Ca
2+
influx is controlled by the status of Ca
2+
loading of intracellular Ca
2+
stores in human aortic endothelial cells.
Publisher
Ovid Technologies (Wolters Kluwer Health)
Subject
Cardiology and Cardiovascular Medicine,Physiology
Cited by
33 articles.
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