Elementary events of agonist-induced Ca2+ release in vascular endothelial cells

Abstract

The subcellular spatial and temporal organization of agonist-induced Ca2+ signals was investigated in single cultured vascular endothelial cells. Extracellular application of ATP initiated a rapid increase of intracellular Ca2+ concentration ([Ca2+]i) in peripheral cytoplasmic processes from where activation propagated as a [Ca2+]iwave toward the central regions of the cell. The average propagation velocity of the [Ca2+]iwave in the peripheral processes was 20–60 μm/s, whereas in the central region the wave propagated at <10 μm/s. The time course of the recovery of [Ca2+]idepended on the cell geometry. In the peripheral processes (i.e., regions with a high surface-to-volume ratio) [Ca2+]ideclined monotonically, whereas in the central region [Ca2+]idecreased in an oscillatory fashion. Propagating [Ca2+]iwaves were preceded by small, highly localized [Ca2+]itransients originating from 1- to 3-μm-wide regions. The average amplitude of these elementary events of Ca2+ release was 23 nM, and the underlying flux of Ca2+ amounted to ∼1–2 × 10−18mol/s or ∼0.3 pA, consistent with a Ca2+ flux through a single or small number of endoplasmic reticulum Ca2+-release channels.