Affiliation:
1. From Zentrum der Physiologie, Klinikum der JWG-Universität, Frankfurt/Main, Germany.
Abstract
Abstract
The activation of endothelial cells following exposure to a variety of receptor-dependent and -independent stimuli is associated with the release of Ca
2+
from intracellular stores as well as the influx of Ca
2+
from the extracellular space. In the present study, we investigated the interaction between Ca
2+
signaling in cultured human umbilical vein endothelial cells and tyrosine phosphorylation. Stimulation of endothelial cells with either bradykinin (100 nmol/L), histamine (1 μmol/L), or the Ca
2+
-ATPase inhibitor thapsigargin (30 nmol/L) resulted in a slightly delayed but prolonged tyrosine phosphorylation of two low molecular weight proteins (≈42 and ≈44 kD). These proteins were identified by immunoprecipitation as the 42- and 44-kD isoforms of mitogen-activated protein kinase (MAP kinase). The agonist-induced tyrosine phosphorylation of the 42-/44-kD doublet was sensitive to the tyrosine kinase inhibitors genistein (100 μmol/L) and piceatannol (10 μmol/L) and was inhibited by the removal of Ca
2+
from the extracellular medium. In fura 2–loaded endothelial cells, inhibition of tyrosine kinases attenuated Ca
2+
signaling after stimulation with either bradykinin (30 nmol/L) or thapsigargin (30 nmol/L). Since inhibition of tyrosine kinases specifically attenuates the plateau phase of the Ca
2+
response after stimulation, the effect of tyrosine kinase inhibition appeared to be mostly associated with the influx of Ca
2+
from the extracellular space. These data demonstrate that the signal transduction cascade initiated by receptor-dependent and -independent stimulation of endothelial cells includes the following: a tyrosine kinase inhibitor–sensitive transmembranous influx of Ca
2+
and the tyrosine phosphorylation of two cytosolic protein substrates identified as MAP kinases. Furthermore, on one hand, an increase in [Ca
2+
]
i
was essential for tyrosine phosphorylation; on the other, the Ca
2+
influx was modulated by tyrosine phosphorylation. This finding documents the mutual dependence of these two crucial signaling pathways in endothelial cells.
Publisher
Ovid Technologies (Wolters Kluwer Health)
Subject
Cardiology and Cardiovascular Medicine,Physiology
Cited by
170 articles.
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