DISTRIBUTION OF RECEPTORS MEDIATING PHOSPHOINOSITIDE HYDROLYSIS IN CULTURED HUMAN UMBILICAL ARTERY SMOOTH-MUSCLE AND ENDOTHELIAL-CELLS

Cultures of human umbilical artery smooth muscle and endothelial cells have been established and the effect of a range of calcium-mobilizing receptor agonists on inositol phospholipid hydrolysis has been compared in the two cell types. In human umbilical artery endothelial cells, histamine (EC(50) 20 mu M), ATP (EC(50) 6.7 mu M), sodium fluoride (20 mM) and thrombin (1 U/mL) produced marked increases in [H-3]inositol phosphate accumulation. In contrast, bradykinin (1 mu M), 5-hydroxytryptamine (5-HT) (0.1 mM) and carbachol (1 mM) produced only a small (<1% of the response to 1 mM histamine) effect on [H-3]inositol phosphate accumulation in these cells. In human umbilical artery smooth muscle cells, histamine (EC(50) 16 mu M), bradykinin (EC(50) 4.5 nM), 5-HT (EC(50) 0.7 mu M) and carbachol (EC(50) 21 mu M) produced substantial effects (>20% of the response to 1 mM histamine) on inositol phospholipid hydrolysis while ATP (1 mM) and thrombin (1 U/mL) were much less effective. The response to histamine in both smooth muscle and endothelial cells was antagonized by 50 nM mepyramine (apparent K-d = 5.6 and 2.9 nM in the two cell types, respectively). The response to 5-HT in smooth muscle cells was antagonized by 50 nM ketanserin (apparent K-d = 4.5 nM). In human umbilical artery smooth muscle cells the inositol phosphate response to carbachol was antagonized by 4-diphenylacetoxy-N-methylpiperidine (4-DAMP; pK(d) = 9.3), atropine (pK(d) = 9.7), pirenzepine (pK(d) = 6.7) and methoctramine (pK(d) = 6.9). These data are consistent with the involvement of an M(3)-muscarinic receptor in this response. These studies suggest that receptors mediating inositol phospholipid hydrolysis are differentially distributed betwen human umbilical artery endothelial and smooth muscle cells.