Extracellular nucleotides induce vasodilatation in human arteries via prostaglandins, nitric oxide and endothelium-derived hyperpolarising factor

Abstract

1. The present study was aimed at examining P2 receptor-mediated vasodilatation in human vessels. The isometric tension was recorded in isolated segments of the human left internal mammary artery branches precontracted with 1 microM noradrenaline. 2. Endothelial denudation abolished the dilator responses. 3. The selective P2Y(1) agonist, 2-MeSADP, induced a potent vasodilatation (pEC(50)=6.9+/-0.1). The P2Y(1) antagonist of 10 microM, MRS 2216, shifted the 2-MeSADP concentration-response curve 1.1 log units to the right. The combined P2Y(1) and P2X agonist, 2-MeSATP, stimulated a dilatation with a potency similar to that of 2-MeSADP. Furthermore, MRS 2216 had a similar antagonistic effect on both 2-MeSATP and 2-MeSADP indicating that P2X receptors do not mediate vasodilatation. 4. Both the P2Y(2/4) agonist, UTPgammaS and the P2Y(6) agonist, UDPbetaS, stimulated potent dilatations (pEC(50)=7.8+/-0.4 for UTPgammaS and 8.4+/-0.2 for UDPbetaS). 5. The 2-MeSADP-induced nitric oxide (NO)-mediated dilatation was studied in the presence of 10 micro M indomethacin, 50 nM charybdotoxin and 1 microM apamin. The involvement of the endothelium-derived hyperpolarising factor (EDHF) was investigated in the presence of 0.1 mM L-NOARG and indomethacin. The involvement of prostaglandins was investigated in the presence of L-NOARG, charybdotoxin and apamin. Both NO, EDHF and prostaglandins mediated 2-MeSADP dilatation with similar efficacy (E(max)=25+/-5% for NO, 25+/-6% for EDHF and 27+/-5% for prostaglandins). 6. In conclusion, extracellular nucleotides induce endothelium-derived vasodilatation in human vessels by stimulating P2Y(1), P2Y(2/4) and P2Y(6) receptors, while P2X receptors are not involved. Endothelial P2Y receptors mediate dilatation by release of EDHF, NO and prostaglandins.

Figure 1

Concentration-dependent dilatation in response to 2-MeSADP and 2-MeSATP with and without pretreatment with the P2Y₁ receptor antagonist MRS 2216 (10 μM). The nucleotides were added after desensitisation of P2X₁ receptors with αβ-MeATP (10 μM). The dilatations are expressed as percentage relaxation of an initial precontraction induced by NA (1 μM). Data are shown as means±s.e.m.

Figure 2

The myograph registration of NA (1 μM) contraction followed by concentration-dependent dilatation to 2-MeSADP with (a) and without (b) pretreatment with the P2Y₁ receptor antagonist MRS 2216 (10 μM). The time points for the addition of the respective concentrations of 2-MeSADP are marked in the figure by broken lines. The nucleotides were added after desensitisation of P2X₁ receptors with αβ-MeATP (10 μM).

Figure 3

Concentration-dependent dilatation stimulated by UDPβS and UTPγS in human LIMA branches, after desensitisation of P2X₁ receptors with αβ-MeATP (10 μM). The dilatations are expressed as percentage of an initial precontraction induced by noradrenaline (1 μM). Data are shown as means±s.e.m.

Figure 4

Concentration-dependent dilatation induced by 2-MeSADP after desensitisation of P2X₁ receptors with αβ-MeATP (10 μM). (a) Dilatation induced by 2-MeSADP. (b) Dilatation induced by 2-MeSADP in the presence of 10 μM indomethacin, 50 nM charybdotoxin and 1 μM apamin. (c) The dilatation induced by 2-MeSADP in the presence of 10 μM indomethacin and 0.1 mM L-NOARG. (d) Dilatation induced by 2-MeSADP in the presence of 0.1 mM L-NOARG, 50 nM charybdotoxin and 1 μM apamin. (e) Dilatation induced by 2-MeSADP in the presence of 10 μM indomethacin, 0.1 mM L-NOARG, 50 nM charybdotoxin and 1 μM apamin. The dilatations are expressed as percentage of an initial precontraction induced by noradrenaline (1 μM). Data are shown as means±s.e.m.

Figure 5

Concentration-dependent dilatation in response to 2-MeSADP after desensitisation of P2X₁ receptors with αβ-MeATP (10 μM). (a) Dilatation induced by 2-MeSADP. (b) Dilatation induced by 2-MeSADP in the presence of 0.1 mM L-NOARG. (c) Dilatation induced by 2-MeSADP in the presence of 10 μM indomethacin. (d) Dilatation induced by 2-MeSADP in the presence of 50 nM charybdotoxin and 1 μM apamin. (e) Dilatation induced by 2-MeSADP in the presence of 0.1 mM L-NOARG, 10 μM indomethacin, 50 nM charybdotoxin and 1 μM apamin. The dilatations are expressed as percentage of an initial precontraction induced by noradrenaline (1 μM). Data are shown as means±s.e.m.