Loss of receptor-mediated 86Rb efflux from pig aortic endothelial cells in culture

P2Y- and P2U-mediated increases in internal calcium in single bovine aortic endothelial cells in primary culture

Increases in intracellular calcium ([Ca2+]i) to ATP, ADP, AMP, adenosine, UTP, 2-methylthio ATP (2-MeSATP), 2-methylthio ADP (2-MeSADP) and alpha,beta-methylene ATP (alpha,beta-meATP) were investigated in single bovine aortic endothelial cells (BAEC) in primary culture using Indo-1. Evidence was obtained for the presence of P2Y and P2U, but not P2X receptors. Normalized concentration-effect curves for ATP, UTP and 2-MeSATP were biphasic in shape. At 10 nM, the agonist rank order was UTP > ATP approximately 2-MeSATP, while above 1 microM, it was ATP > or = UTP > or = 2-MeSATP. No cross-desensitization between responses to P2U and P2Y receptors was observed in normal external solution. However, when internal Ca2+ stores were depleted by exposure to 2-MeSATP or UTP in Ca2+-free solution and agonists then re-applied in presence of external Ca2+, homologous but not heterologous desensitization was seen. In the same conditions, heterologous desensitization was observed for UTP after ATP but not for ATP after UTP. Taken together, the results are consistent with the coexistence of P2Y and P2U receptors in primary-cultured BAEC and suggest that upon activation, different intracellular signaling pathways could be involved in increasing [Ca2+]i.

Altered expression of cyclic nucleotide phosphodiesterase isozymes during culture of aortic endothelial cells

Primary cultures of bovine aortic endothelial cells (BAEC) express cyclic nucleotide phosphodiesterase (CN PDE) isozymes of the PDE2, PDE4 and PDE5 gene families. We report here that the isozyme profiles of CN PDE and the amounts of each vary with the passage number of BAEC cultures. Characterization by anion-exchange chromatography and pharmacological criteria were used to study CN PDE in early (4-6), intermediate (6-10), and late (> 17) passages of purified BAEC. PDE2 and a minor fraction of PDE5 accounted for cyclic GMP hydrolysis in early passages, but both isozymes were lost with cell passage. Cyclic AMP was hydrolyzed by both PDE2 and PDE4 isozymes in early passage endothelial cells, but PDE4 was increased dramatically in higher passage cells. Also appearing in the higher passage cells were prominent PDE1 and minor PDE3 activities. The ratios of cytosolic to particulate activities were similar at all passages. BAEC PDE isoforms in intact cells assessed by [3H]-adenine prelabeling showed that atriopeptin II decreased isoproterenol-induced cyclic AMP accumulation in early but not later passage cells, consistent with the loss of PDE2 expression. Enhancement of isoproterenol-induced cyclic AMP accumulation by rolipram, a PDE4 inhibitor, was also greatly diminished during culture passages. Changes in CN PDE isoform expression and consequent cyclic AMP turnover validate the importance of considering cell passage number when cultures of BAEC are used to study the regulation of endothelial cell cyclic nucleotide metabolism and processes mediated by cyclic nucleotides in this model system.

The effect of endothelins on nitric oxide and prostacyclin production from human umbilical vein, porcine aorta and bovine carotid artery endothelial cells in culture

1. This study has investigated the effects of the endothelin isopeptides, endothelin-1 (ET-1), ET-2 and ET-3 on the production of the endothelium-derived relaxing factors, nitric oxide (NO) and prostacyclin (PGI2) from primary cultures of endothelial cells obtained from human umbilical vein (HUVECS), porcine aorta (PAECS) and bovine carotid artery (BCAECS). 2. NO generation was assessed indirectly by measuring production of cyclic GMP and PGI2 formation was measured by radioimmunoassay of 6-keto PGF1 alpha. 3. In HUVECS, histamine (1 microM) increased cyclic GMP and 6-keto PGF1 alpha production by 12.6 +/- 2.0 and 4.9 +/- 0.7 fold respectively over the corresponding basal values. Haemoglobin (10 microM) and the NO synthase inhibitor NG-monomethyl-L-arginine (10 microM) significantly inhibited the increase in cyclic GMP formation in response to histamine but had no effect on 6-keto PGF1 alpha production. In contrast to histamine, the endothelin isopeptides (ET-1, ET-2 and ET-3; 0.01-1000 nM) produced no significant change in either cyclic GMP or 6-keto PGF1 alpha production in HUVECS. 4. In a separate series of experiments, ET-3 (0.01-1000 nM) also failed to produce any significant change in cyclic GMP or 6-keto PGF1 alpha production from primary cultures of PAECS and BCAECS. In contrast, bradykinin (0.1 microM) and sodium nitroprusside (1 mM) were used as positive control agents and increased cyclic GMP production in these cells. 5. In conclusion, the endothelin isopeptides do not release NO and PGI2 from primary cultures of HUVECS, PAECS and BCAECS. This suggests that endothelin receptors are either absent from these cells or are not coupled to NO or PGI2 production.

Endothelium-derived relaxing factor and atriopeptin II elevate cyclic GMP levels in pig aortic endothelial cells

1. Two directly-acting stimulants of soluble guanylate cyclase, glyceryl trinitrate (0.1 microM) and sodium azide (10 microM), and a receptor-mediated stimulant of particulate guanylate cyclase, atriopeptin II (10 nM), each elevated the cyclic GMP content of primary cultures of pig aortic endothelial cells without affecting the cyclic AMP content. 2. Two receptor-mediated stimulants of adenylate cyclase, glucagon (1 microM) and isoprenaline (10 microM), had no effect on the cyclic AMP or cyclic GMP content of these cells, but the directly acting stimulant, forskolin (30 microM), induced a small increase in cyclic AMP content. 3. Three agents that release endothelium-derived relaxing factor (EDRF); bradykinin (0.1 microM), ATP (10 microM) and ionophore A23187 (0.1 microM), each markedly elevated the cyclic GMP content of pig aortic endothelial cells, but acetylcholine (1 microM) had no effect. None of these agents had any effect on cyclic AMP content. 4. Two agents that potentiate the actions of EDRF; M & B 22948 (100 microM) and superoxide dismutase (30 units ml-1), each elevated the cyclic GMP content of pig aortic endothelial cells without affecting the cyclic AMP content. Pretreating cells with catalase (100 units ml-1) did not affect the rise in cyclic GMP content induced by superoxide dismutase (30 units ml-1). 5. Pretreatment of pig aortic endothelial cells with haemoglobin (10 microM) reduced the resting content of cyclic GMP and blocked the increase in cyclic GMP content induced by glyceryl trinitrate (0.1 microM), sodium azide (10 microM), bradykinin (0.1 microM), ATP (10 microM), ionophore A23187 (0.1 microM), M & B 22948 (100 microM) and superoxide dismutase (30 units ml-1), but not that induced by atriopeptin II (10 nM). 6. Pretreatment of pig aortic endothelial cells with an inhibitor of soluble guanylate cyclase, methylene blue (20 microM), had no effect on the resting content of cyclic GMP. Methylene blue (20 microM) blocked the increase in cyclic GMP content induced by glyceryl trinitrate (0.1 microM), M & B22948 (100 microM) and bradykinin (0.1 microM), but not that induced by atriopeptin II (10 nM). 7. The data show that soluble guanylate cyclase, particulate guanylate cyclase and adenylate cyclase are present in pig aortic endothelial cells. They further suggest that EDRF, produced spontaneously or in response to vasoactive agents, elevates endothelial cyclic GMP content by stimulating soluble guanylate cyclase. It is possible that this may serve as a feedback loop by which the endothelial cell modulates EDRF production.

Characteristics of the P2 purinoceptor that mediates prostacyclin production by pig aortic endothelial cells

Release of prostacyclin was studied by superfusing small columns containing cells cultured on microcarrier beads. Transient dose-dependent stimulation of prostacyclin release by up to 500-fold was induced by adenosine 5'-triphosphate (ATP; 0.5-50 microM). Adenosine 5'-diphosphate (ADP) gave similar responses, whereas adenosine 5'-phosphate (AMP) and adenosine were essentially inactive. Of other natural nucleotides tested only uridine 5'-phosphate (UTP) was active. The L-enantiomers of ATP and ADP were inactive. 2-Cl-ATP was approximately 100 times more potent than ATP; 2-MeS-ATP was also more potent (threshold 0.05 microM) but its maximal effectiveness was less than 20% that of ATP; 2-EtS-ATP had a similar threshold to ATP but was even less effective than 2-MeS-ATP. Phosphorothioate nucleotide analogues of ATP or ADP were active, with no stereoselectivity between Rp and Sp diastereoisomers. No analogue tested showed antagonist activity. We conclude that ATP mediates endothelial prostacyclin release apparently via a P2Y receptor, although there are some striking differences from the previously described P2Y receptor mediating endothelium-dependent vasodilation in pig aorta.

Anaphylatoxin C5a fails to promote prostacyclin release in cultured endothelial cells from human umbilical veins

Subcultured endothelial cells from human umbilical veins respond to histamine and melittin with increased prostacyclin production, measured as 6-keto-prostaglandin F1 alpha by radioimmunoassay. However, no response to leukotriene C4 was observed. Primary cultured cells, on the other hand, respond to leukotriene C4 and the histamine response was 7 times more potent for these cells than for subcultured cells. In contrast, neither primary cultures nor subcultures of endothelial cells released prostacyclin following application of either human anaphylatoxin C5a (100 nM) or C3a (1 microM). In addition, these endothelial cells appear to have no specific binding sites for 125I-C5a. However, endothelial cells released prostacyclin in the presence of human polymorphonuclear leukocytes that were activated with C5a. We conclude that involvement of endothelial cells in the haemodynamic response to anaphylatoxin is an indirect function, i.e. C5a activates circulating or tissue cells which in turn stimulate the endothelial cell to produce prostacyclin.