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Evidence for the existence of inositol (1,4,5)-trisphosphate- and ryanodine-sensitive pools in bovine endothelial cells. Ca2+ releases in cells with different basal level of intracellular Ca2+
Authors:Marina G Mozhayeva  Galina N Mozhayeva
Institution:(1) Department of Physiological Sciences The Medical School, The University, Newcastle Upon Tyne, NE2 4HH, UK, GB;(2) From the Institute of Cytology, Russian Academy of Sciences, Tikhoretsky Ave. 4, 194064 St. Petersburg, Russia, RU
Abstract:In single bovine aortic endothelial (BAE) cells pre-loaded with Fura-2, Ca2+ transients in a Ca2+-free medium have been revealed, which evidently reflects Ca2+ release from intracellular stores. In cells with different levels of resting basal cytoplasmic Ca2+ (Ca2+]i) from about 50 to 110 nM, a biphasic dependence of the Ca2+ transients on resting Ca2+]i was shown and spontaneous Ca2+ oscillations were observed. At a Ca2+]i level over 110 nM, a pronounced rise in Ca2+ transients occurred and only single transients were observed. Ryanodine (10 μM) produced a transient Ca2+]i elevation, suggesting the presence of ryanodine receptors in intracellular store membranes. The results imply that both inositol 1,4,5-trisphosphate-sensitive Ca2+ release (IICR) and Ca2+-sensitive Ca2+ release (CICR) take place in BAE cells. Only IICR seems to be sufficient for generating baseline Ca2+ oscillations in BAE cells, whereas the ATP-induced (5–100 μM) Ca2+ response involves the CICR set in motion by an oscillatory IICR of high frequency. The completion of both the spontaneous and ATP-induced Ca2+ transients was associated with a Ca2+]i decrease to a level below the initial resting Ca2+]i (undershoot). Its depth biphasically depended on the resting Ca2+]i from 50 to 110 nM, suggesting that the lack of a Ca2+ leak from inositol 1,4,5-trisphosphate-sensitive stores is responsible for the undershoot in this range. The Ca2+ leak is concluded to play a key role in the initiation and termination of regenerative IICR both in spontaneous oscillations and in ATP-induced transients. Received: 13 November 1995/Received after revision and accepted 27 March 1996
Keywords:Intracellular Ca2+  Endothelial cells  Fura-2  Calcium oscillations  ATP  Ryanodine
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