Histamine induced alteration of calcium binding to microvascular endothelium as indicated by use of ionic lanthanum.

To determine whether histamine's effect on microvascular permeability might be associated with altered calcium binding, the influence of histamine on lanthanum binding to vascular endothelium was assessed in the presence of verapamil. Isolated rabbit hearts were perfused firstly with histamine, secondly with histamine and verapamil, and subsequently with histamine in the presence of lanthanum and verapamil. Examination by transmission electron microscopy showed that 92% of microvessels examined contained bound lanthanum on plasma membranes, plasmalemmal vesicles, or endothelial clefts of vascular endothelium, or all three, in both atria and ventricles, which is in contrast to the low proportion (4%) of microvessels containing bound lanthanum found in the presence of verapamil alone. The enhancement of lanthanum binding was reduced by both H1 and H2 receptor antagonists. This evidence supports the hypothesis that the increase in vascular permeability with histamine may be associated with increased calcium binding to vascular endothelial membranes and that both H1 and H2 receptors play a part in this activity.