Histamine type I receptor occupancy increases endothelial cytosolic calcium, reduces F-actin, and promotes albumin diffusion across cultured endothelial monolayers.
Considerable evidence suggests that Ca2+ modulates endothelial cell metabolic and morphologic responses to mediators of inflammation. We have used the fluorescent Ca2+ indicator, quin2, to monitor endothelial cell cytosolic free Ca2+, [Ca2+]i, in cultured human umbilical vein endothelial cells. Histamine stimulated an increase in [Ca2+]i from a resting level of 111 +/- 4 nM (mean +/- SEM, n = 10) to micromolar levels; maximal and half-maximal responses were elicited by 10(-4) M and 5 X 10(-6) M histamine, respectively. The rise in [Ca2+]i occurred with no detectable latency, attained peak values 15-30 s after addition of stimulus, and decayed to a sustained elevation of [Ca2+]i two- to threefold resting. H1 receptor specificity was demonstrated for the histamine-stimulated changes in [Ca2+]i. Experiments in Ca2+-free medium and in the presence of pyrilamine or the Ca2+ entry blockers Co2+ or Mn2+, indicated that Ca2+ mobilization from intracellular pools accounts for the initial rise, whereas influx of extracellular Ca2+ and continued H1 receptor occupancy are required for sustained elevation of [Ca2+]i. Ionomycin-sensitive intracellular Ca2+ stores were completely depleted by 4 min of exposure to 5 X 10(-6) M histamine. Verapamil or depolarization of endothelial cells in 120 mM K+ did not alter resting or histamine-stimulated [Ca2+]i, suggesting that histamine-elicited changes are not mediated by Ca2+ influx through voltage-gated channels. Endothelial cells grown on polycarbonate filters restricted the diffusion of a trypan blue-albumin complex; histamine (through an H1-selective effect) promoted trypan blue-albumin diffusion with a concentration dependency similar to that for the histamine-elicited rise in [Ca2+]i. Exposure of endothelial cells to histamine (10(-5) M) or ionomycin (10(-7) M) was associated with a decline in endothelial F-actin (relative F-actin content, 0.76 +/- 0.07 vs. 1.00 +/- 0.05; histamine vs. control, P less than 0.05; relative F-actin content, 0.72 +/- 0.06 vs. 1.00 +/- 0.05; ionomycin vs. control, P less than 0.01). The data support a role for cytosolic calcium in the regulation of endothelial shape change and vessel wall permeability in response to histamine.
D000199:Actins / Q000378:metabolism*; D000634:Aminoquinolines; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D004058:Diffusion; D004727:Endothelium / Q000187:drug effects / Q000378:metabolism*; D006632:Histamine / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D011968:Receptors, Histamine / Q000502:physiology*; D011969:Receptors, Histamine H1 / Q000502:physiology*; D012710:Serum Albumin, Bovine / Q000378:metabolism*; D014471:Umbilical Veins
D000199:Actins; D000634:Aminoquinolines; D011968:Receptors, Histamine; D011969:Receptors, Histamine H1; D012710:Serum Albumin, Bovine; D006632:Histamine; C035739:Quin2; D002118:Calcium