Extracellular adenosine triphosphate (ATP) is known to open a receptor‐operated ion channel (P2Z class) in human lymphocytes which conducts a range of cationic permeants. The activity of a range of different agonists and inhibitors towards the P2Z‐purinoceptor was investigated by measuring the agonist‐induced influx of Ba2+ into fura‐2 loaded lymphocytes. The most potent agonist was 2′ & 3′‐0‐(4‐benzoylbenzoyl)‐ATP (benzoylbenzoic ATP) which gave 2 fold greater maximum Ba2+ influx and had a 10 fold lower EC50 than for ATP. The rank order of agonist potency in K+‐media was benzoylbenzoic ATP>>ATP = 2‐methylthio ATP = 2‐chloro ATP>ATP‐γ‐S. ADP, UTP and α,β‐methylene ATP were unable to stimulate Ba2+ influx. Extracellular Na+ inhibited the increment of Ba2+ influx induced by all concentrations of ATP, 2‐methylthio ATP, 2‐chloroATP and ATP‐γ‐S. This inhibitory effect of extracellular Na+ is also reflected in the different EC50s for benzoylbenzoic ATP (8 μm in K+‐media, 18 μm in Na+‐media) but the maximal response to this agonist was the same in the presence or absence of Na+. Treatment of lymphocytes with 2,3 dialdehyde ATP (oxidized ATP) at 300 μm for 60 min gave total and irreversible inhibition of ATP‐induced Ba2+ influx. 5′‐p‐Fluorosulphonyl benzoyladenosine (FSBA) also was an irreversible inhibitor but the maximal inhibition achieved was 90%. It is concluded that the P2Z‐purinoceptor of human lymphocytes has a rank order of agonist potency which clearly distinguishes it from other P2‐receptors and that oxidized ATP is a convenient irreversible inhibitor for the P2Z‐purinoceptor.

Milrinone is an inotropic drug with vasodilator activity that has been shown to be useful in increasing cardiac output and decreasing wedge pressure. Despite these advantages, it is unknown whether this drug can be used for the treatment of perioperative spasm of coronary bypass grafts. This study was undertaken to investigate the in vitro vascular effect of milrinone on internal thoracic arteries obtained from patients undergoing coronary artery bypass grafting. The results showed that milrinone produced a potent, concentration-dependent, preventive effect on the norepinephrine-induced contraction of internal thoracic arteries, as well as reversing contraction of internal thoracic arteries by receptor-dependent agents, including the thromboxane A2 mimetic U46619, the vasoconstrictor peptide endothelin-1, and the alpha1-adrenal receptor agonist phenylephrine. The relaxing effect of milrinone was weaker, however, on internal thoracic arteries contracted with 25 mmol/L potassium chloride. Comparison of milrinone with other vasodilators, including papaverine, nitroprusside, and glyceryl trinitrate, showed milrinone to be more potent than papaverine but less potent than nitroprusside and glyceryl trinitrate. The inhibitory effect of milrinone on internal thoracic artery contraction appeared as a reduction in contractile force, not as an increase in the values of concentrations of the agonists causing 50% maximal contraction, which indicates that milrinone exerts its vasodilator effect directly on the smooth muscles, not on the membrane receptors. The results also showed no significant difference in relaxing effect between internal thoracic artery rings with and without endothelium. In conclusion, this study provides experimental evidence that milrinone is a potent, endothelium-independent, direct vasodilator of the human internal thoracic artery and provides the scientific rationale for a future clinical trial with this drug for the perioperative treatment of internal thoracic artery spasm in cardiac surgical patients.

Summary.Chronic lymphocytic leukaemia (B-CLL) is characterized by a progressive accumulation of B lymphocytes in blood and bone marrow and high concentrations of soluble CD23 and L-selectin are found in the serum of these patients. In this study lymphocytes from normal subjects and patients with B-CLL were allowed to undergo transendothelial migration across confluent layers of human umbilical vein endothelial cells. Lymphocytes in B-CLL samples showed an impaired capacity to migrate while the minor proportion of normal T cells was enriched by a mean of 2·5-fold in the transmigrated lymphocytes. In contrast, the ratio of B to T lymphocytes in normal preparations was unchanged in the transmigrated population. The expression of adhesion molecules on B-CLL lymphocytes before and after transendothelial migration was studied by flow cytometry which showed that 71 Ϯ 5% of L-selectin was lost from the surface of transmigrated lymphocytes. T and B cells from normal subjects also showed a major loss of L-selectin after transmigration. B-CLL lymphocytes and normal B cells expressed CD23 but this molecule was down-regulated following transendothelial migration, whereas the expression of VLA-4, ICAM-1, LFA-1 and CD44 was unchanged. Lymphocytes incubated with oxidized ATP, an irreversible inhibitor of P2Z/P2X7 purinoceptors, retained their capacity for transendothelial migration and showed the same loss of L-selectin as control leukaemic lymphocytes. Our results show that B-CLL lymphocytes have impaired ability for transendothelial migration compared to normal peripheral blood lymphocytes. Moreover, transendothelial migration involves a universal loss of L-selectin and CD23 from lymphocytes which suggests that the high serum levels of soluble L-selectin and CD23 observed in B-CLL may be generated by shedding during the process of transendothelial migration.

1. The role of the ET(B) receptor in human arteries has not been well studied because of the lack of specific ET(B) receptor antagonists. In the present studies the specific ET(B) receptor antagonist BQ-788 and the specific ET(B) agonist IRL-1620 were used to characterize the function of the ET(B) receptor in human radial arteries and internal mammary arteries. 2. The results showed that the ET(B) antagonist BQ-788 significantly inhibited endothelin-1-induced contraction in internal mammary arteries, but not in radial arteries. In internal mammary arteries, BQ-788 at a concentration of 10 micromol/l shifted the endothelin-1-induced concentration-dependent curve to the right by one order. By comparison, the ET(A) receptor antagonist BQ-610 at 1 micromol/l produced a much more potent inhibitory effect (three-order shifting) on endothelin-1-induced contraction in internal mammary arteries, and also potently inhibited the contraction in radial arteries. 3. The ET(B) agonist IRL-1620 caused a contraction in internal mammary arteries, but not in radial arteries, although the response of radial arteries to endothelin-1 was very strong. The contraction induced by IRL-1620 was weaker than that induced by endothelin-1; however, the maximal contraction to IRL-1620 was obtained at 3 nmol/l, which was lower than that with endothelin-1 (maximal contraction at 10 nmol/l). 4. In internal mammary arteries the contraction to endothelin-1 and IRL-1620 gradually changed to relaxation with high concentrations of endothelin-1 (from 30 nmol/l) and IRL-1620 (from 3 nmol/l), whereas it did not in radial arteries; suggesting that the ETB receptor on human arterial smooth muscle cells may mediate contraction at low agonist concentrations and relaxation at high agonist concentrations. 5. The ET(B) agonist IRL-1620, endothelin-1 and endothelin-3 did not cause endothelium-dependent relaxation in either precontracted radial arteries or internal mammary arteries, although endothelium-dependent relaxation was fully induced by acetylcholine in these two arterial preparations. 6. In conclusion, the present studies demonstrate that the responses of internal mammary arteries and radial arteries to an ET(B) antagonist and an ET(B) agonist are significantly different from those of animal vascular vessels, and also from each other. The ET(B) receptor may play only a minor role in endothelium-dependent relaxation of these human arteries. Endothelin-1-induced contraction is mediated by both the ET(A) (major) and the ET(B) (minor) receptors in internal mammary arteries, but only by the ET(A) receptor in radial arteries. These studies may help to determine therapeutic strategy.