Ca2+ entry through conductive pathway modulates receptor-mediated increase in microvessel permeability

Abstract

We investigated the relationship between receptor-mediated increases in cytoplasmic Ca2+ concentration ([Ca2+]i) and increased microvessel permeability. In individually perfused venular microvessels of frog mesentery exposed to 10 microM ATP, [Ca2+]i increased from 59 +/- 7 to 172 +/- 21 nM within 1 min and then fell back toward control values. The corresponding peak increase in the hydraulic conductivity (Lp) of the microvessel wall was 5.7 +/- 0.5-fold relative to control. After removal of extracellular Ca2+, there was no significant increase in Lp, and the initial increase in [Ca2+]i was attenuated but not abolished. Depolarization of the endothelial cell membrane with high-K+ Ringer solution reduced the peak increase in [Ca2+]i to 106 +/- 7 nM and attenuated the increase in Lp 1.8 +/- 0.4-fold. The results conform to the hypothesis that Ca2+ entry into endothelial cells is required for acute increase in venular microvessel permeability by inflammatory agents and that the pathway for Ca2+ entry has the properties of a passive conductance pathway. Similar conclusions were reached in previous experiments in frog microvessels exposed to Ca2+ ionophores and perfusates with no plasma proteins. In venular microvessels of hamster mesentery exposed to ATP and bradykinin, a similar pathway for Ca2+ entry was demonstrated in the present experiments. We did not measure permeability changes in hamster microvessels in this study, but these microvessels respond to histamine and ionophores with a transient increase in permeability to macromolecules similar to that measured in frog microvessels [Am. J. Physiol. 268 (Heart Circ. Physiol. 37): H1982-H1991, 1995].

Vascular remodeling alters adhesion protein and cytoskeleton reactions to inflammatory stimuli resulting in enhanced permeability increases in rat venules

“…Details have been described (19). In brief, a venular microvessel was cannulated and perfused first with albumin-Ringer solution that contained 10 M of fura-2 AM for 45 min.…”

“…The background FI due to unconverted fura-2 AM and other Ca 2ϩ -insensitive forms of fura-2 were subtracted from FI 340 and FI380 values. The ratios of the two FI values were converted to Ca 2ϩ concentrations using an in vitro calibration curve (19). Confocal imaging.…”

“…Mammalian Ringer solution was used for the experiments (19). The composition of the mammalian Ringer solution was (in mM) 132 NaCl, 4.6 KCl, 2 CaCl2, 1.2 MgSO4, 5.5 glucose, 5.0 NaHCO3, 20 N-2-hydroxyethylpiperazine-N=-2-ethanesulfonic acid and Na-N-2-hydroxyethylpiperazine-N=-2-ethanesul-fonic acid.…”

Calcium influx-dependent differential actions of superoxide and hydrogen peroxide on microvessel permeability

“…A Nikon Diaphod 300 microscope equipped with a Nikon photometry system and a digital cooled charge-coupled device camera (ORCA, Hamamatsu, 12 bit) was used for the experiments. The experimental procedures have been described in detail elsewhere (14,16). In brief, a venular microvessel in rat mesentery was first cannulated and perfused with albumin-Ringer solution containing 10 M fura-2 AM for 45 min in the dark.…”

“…Solutions and reagents. Mammalian Ringer solution was used for dissecting mesenteries, superfusing tissue, and preparing the perfusion solutions (16). The composition of the mammalian Ringer solution was (in mM) 132 NaCl, 4.6 KCl, 2 CaCl 2, 1.2 MgSO4, 5.5 glucose, 5.0 NaHCO3, 20 HEPES, and Na-HEPES.…”