HISTAMINE RECEPTOR-MEDIATED CHANGES IN NUCLEAR CHROMATIN OF CULTURED ENDOTHELIAL AND SMOOTH MUSCLE CELLS

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Histamine, acting via membrane receptors, modulates a number of potentially important processes within the vascular wall. Histamine receptor activation affects cellular activities such as contractility, movement, growth, and metabolism. The present study entails a characterization of endothelial (EC) and smooth muscle cell (SMC) histamine receptors with respect to cytochemical indices of DNA content and chromatin dispersion.
Both EC and SMC exhibited functionally active H₁ and H₂ receptors. Activation of either receptor type resulted in a substantial ploidy shift in EC but not in SMC cultures. The physico-chemical state of chromatin as assessed by Feulgen reactivity was altered in both cell types. H₂ receptor activation elevated Feulgen reactivity in 2C nuclei, while in 4C nuclei both H₁ and H₂ receptors were active in this regard. Elevation of Feulgen reactivity of EC and SMC nuclear chromatin in response to histamine receptor agonists presumably represents a “chromatin activation reaction” reflecting alterations in the conformation of the deoxyribonucleoprotein (DNP) complex and accompanying changes in template activity. Disparity between agonist effects on 2C and 4C populations may reflect the cell cycle regulation of histamine receptors.