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 compar ed 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 (2 0 mM) and thrombin (1 U/mL) produced marked increases in [H-3]inositol phosphate accumulation. In contrast, bradykinin (1 mu M), 5-hydroxytr yptamine (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 phosphat e 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 e ffects (>20% of the response to 1 mM histamine) on inositol phospholip id hydrolysis while ATP (1 mM) and thrombin (1 U/mL) were much less ef fective. The response to histamine in both smooth muscle and endotheli al 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 sm ooth muscle cells was antagonized by 50 nM ketanserin (apparent K-d = 4.5 nM). In human umbilical artery smooth muscle cells the inositol ph osphate response to carbachol was antagonized by 4-diphenylacetoxy-N-m ethylpiperidine (4-DAMP; pK(d) = 9.3), atropine (pK(d) = 9.7), pirenze pine (pK(d) = 6.7) and methoctramine (pK(d) = 6.9). These data are con sistent with the involvement of an M(3)-muscarinic receptor in this re sponse. These studies suggest that receptors mediating inositol phosph olipid hydrolysis are differentially distributed betwen human umbilica l artery endothelial and smooth muscle cells.