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FMLP actions and its binding sites in isolated human coronary arteries
M Keitoku1, M Kohzuki, H Katoh
1First Department of Internal Medicine, Tohoku University School of Medicine, Sendai, Japan.
Abstract:
The chemoattractant f-Met-Leu-Phe (FMLP) can modulate human coronary arterial tone without the involvement of peripheral leukocytes. We investigated the actions of FMLP and its cellular mechanism in human coronary arteries isolated 2-3 h after death. A single dose of FMLP (0.01-10 microM) produced transient contraction (or, followed by relaxation) responses in most human coronary rings examined. These responses to FMLP were in large part mediated by the generation of cyclooxygenase products, mainly thromboxane A2 (TXA2) and prostaglandin I2 (PGI2). Radiolabeled N-formyl hexapeptide. 125I-f-Nle-Leu-Phe-Nle-Tyr-Lys bound densely to intimal and adventitial sites that accumulated macrophages (CD68-positive) with a Kd of 14-29 nM and, further, weakly to the media with a Kd of 2.4-3.6 microM. Several cell types including macrophages, endothelial cells and smooth muscle cells were positively immunostained for both TXA2 synthase and PGI2 synthase. However, there was no significant relation between the magnitude of the responses to FMLP and dense macrophage accumulation in the intimal plaques or the adventitia. A reverse transcription-polymerase chain reaction showed predominant expression of FMLP receptor homologues, FPRH1 and FPRH2 mRNA, in human coronary medial tissues relative to that in leukocytes. In conclusion. FMLP produced transient tension changes in human coronary arteries, mainly via the generation of TXA2 and PGI2. This effect of FMLP did not appear to be mediated by the activation of densely accumulated intimal and/or adventitial macrophages, but by the activation of unidentified medial tissue cells which might have functional FMLP receptor homologues.
Insights
The chemoattractant f-Met-Leu-Phe (FMLP) alters human coronary artery tone via thromboxane A2 and prostaglandin I2. This effect involves medial cells, not intimal macrophages, suggesting novel FMLP receptor actions.
Area of Science:
- Cardiovascular Biology
- Immunology
- Pharmacology
Background:
- The chemoattractant formylated tripeptide, f-Met-Leu-Phe (FMLP), is known to influence vascular tone.
- Its precise cellular mechanisms within human coronary arteries, independent of circulating leukocytes, remain incompletely understood.
Purpose of the Study:
- To investigate the effects of FMLP on human coronary arterial tone.
- To elucidate the cellular and molecular mechanisms underlying FMLP-induced responses in these vessels.
Main Methods:
- Human coronary artery rings were isolated and exposed to FMLP.
- Vascular responses were measured, and cyclooxygenase product generation was assessed.
- Radioligand binding, immunostaining, and RT-PCR were used to identify cell types and receptor expression.
Main Results:
- FMLP induced transient contraction or relaxation in human coronary artery rings.
- These responses were largely mediated by thromboxane A2 (TXA2) and prostaglandin I2 (PGI2) generation.
- FMLP receptors (FPRH1, FPRH2 mRNA) were predominantly expressed in medial tissues, not intimal macrophages.
Conclusions:
- FMLP modulates human coronary arterial tension primarily through TXA2 and PGI2 production.
- The observed effects are mediated by unidentified medial cells expressing FMLP receptor homologues, rather than by accumulated macrophages.