The Volatile Anesthetic Isoflurane Inhibits the Histamine-Induced Ca2+ Influx in Primary Human Endothelial Cells

Although isoflurane is a known vasodilator, the mechanism of isoflurane-induced vasodilation is not clear. One of the most important systems in this context is the nitric oxide (NO)-mediated vasodilation. The activity of this system is regulated by the agonist-induced Ca2+ influx rather than Ca2+ release from internal stores. A number of reports have studied the effect of volatile anesthetics on the cytoplasmic calcium concentration signaling in mammalian endothelial cells. However, similar studies using human endothelial cells are lacking. In this study, therefore, we investigated whether isoflurane affects the histamine-induced Ca2+ influx in primary cultures of human endothelial cells. Using confocal laser scanning microscopy and cells loaded with the Ca2+ indicator Fluo-3, we studied the effect of isoflurane on the plateau phase of the histamine-induced Ca2+ influx, which is considered to be due to capacitative Ca2+ entry. In addition, we measured the ion flux through capacitative Ca2+ channels directly by using Mn2+ ions, which, on entering the cell, quench the Fura-2 fluorescence. The results of these two methods were in close agreement and showed a dose-dependent inhibition of the capacitative Ca2+ entry by isoflurane. Isoflurane apparently depresses NO-mediated vasodilation when the observed inhibition is not compensated for downstream of the endothelial NO synthase activation.