Key result
Microvascular permeability in vivo can be increased by agents that release Ca2+ from stores in the absence of Ca2+ influx, and capacitative Ca2+ entry further increases hydraulic conductivity.
Microvascular permeability in vivo can be increased by agents that release Ca2+ from stores even in the absence of Ca2+ influx, and capacitative Ca2+ entry further increases permeability.
Hypothesis-generating for Ca2+ pathways in vascular leak; leaves open translation to human microvascular disease.
Vascular permeability is regulated by endothelial cytosolic Ca(2+) concentration ([Ca(2+)](i)). To determine whether vascular permeability is dependent on extracellular Ca(2+) influx or release of Ca(2+) from stores, hydraulic conductivity (L(p)) was measured in single perfused frog mesenteric microvessels in the presence and absence of Ca(2+) influx and store depletion. Prevention of Ca(2+) reuptake into stores by sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) inhibition increased L(p) in the absence of extracellular Ca(2+) influx. L(p) was further increased when Ca(2+) influx was restored. Depletion of the Ca(2+) stores with ionomycin and SERCA inhibition increased L(p) in the presence and the absence of extracellular Ca(2+) influx. However, store depletion in itself did not significantly increase L(p) in the absence of active Ca(2+) release from stores into the cytoplasm. There was a significant positive correlation between baseline permeability and the magnitude of the responses to both Ca(2+) store release and Ca(2+) influx, indicating that the Ca(2+) regulating properties of the endothelial cells may regulate the baseline L(p). To investigate the role of Ca(2+) stores in regulation of L(p), the relationship between SERCA inhibition and store release was studied. The magnitude of the L(p) increase during SERCA inhibition significantly and inversely correlated with that during store release by Ca(2+) ionophore, implying that the degree of store depletion regulates the size of the increase on L(p). These data show that microvascular permeability in vivo can be increased by agents that release Ca(2+) from stores in the absence of Ca(2+) influx. They also show that capacitative Ca(2+) entry results in increased L(p) and that the size of the permeability increase can be regulated by the degree of Ca(2+) release.
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Glass et al. (2003) studied this question. SERCA inhibition and store depletion vs. Baseline / absence of Ca2+ influx was evaluated on Hydraulic conductivity (L(p)). Microvascular permeability in vivo can be increased by agents that release Ca2+ from stores in the absence of Ca2+ influx, and capacitative Ca2+ entry further increases hydraulic conductivity.
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