Imaging of Ca2+ transients in endothelial cells of single perfused capillaries: correlation of peak [Ca2+]i with sites of macromolecule leakage.
OBJECTIVE
To investigate the mechanisms responsible for variation in the macromolecular leakage (formation of localized leaky sites) in venular microvessels with increased permeability, we examined the hypothesis that cytoplasmic calcium concentration [Ca2+]i, does not increase uniformly within microvessel endothelial cells.


METHODS
We loaded the endothelial cells forming the walls of venular microvessels in frog mesentery with fura-2, and imaged [Ca2+]i using a cooled CCD camera.


RESULTS
Control [Ca2+]i was close to 60 nM in all regions. Control permeability was uniformly low in all microvessels. Exposure to ionomycin (5 mM) increased [Ca2+]i in a biphasic manner, but not uniformly. There was variation in both time to peak (bimodal distribution) and peak [Ca2+]i (274 +/- 13 nM; mean variation above or below the peak value was 110 nM). Raising extracellular calcium from 1.1 to 5 mM increased the mean variation of [Ca2+]i about peak values. Extravascular leakage of fluorescently labeled albumin or low-density lipoproteins was most prominent at sites where increase in [Ca2+]i were largest.


CONCLUSIONS
These data indicate that variation in [Ca2+]i within individual endothelial cells or groups of cells could account, at least in part, for the distribution of localized leakage sites for macromolecules in venular microvessels in the high-permeability state.
Pagakis
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Department of Human Physiology, School of Medicine, University of California, Davis 95616, USA.
Curry
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D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002199:Capillary Permeability; D004730:Endothelium, Vascular / Q000378:metabolism / Q000648:ultrastructure*; D005456:Fluorescent Dyes; D016257:Fura-2; D007091:Image Processing, Computer-Assisted; D008297:Male; D008856:Microscopy, Fluorescence; D018715:Microscopy, Video; D011894:Rana pipiens; D013997:Time Factors
D005456:Fluorescent Dyes; D002118:Calcium; D016257:Fura-2