title: Mechanisms responsible for the in vitro relaxation of ligustrazine on porcine left anterior descending coronary artery.
abstract: In this study, we have evaluated the underlying mechanisms responsible for the relaxation response of ligustrazine (2,3,5,6-tetra-methyl-pyrazine; 2,3,5,6-MP) and its structural analogues (2-methyl-pyrazine (2-MP); ethyl-pyrazine (EP); 2,3-di-methyl-pyrazine (2,3-MP); 2,5-di-methyl-pyrazine (2,5-MP); 2,6-di-methyl-pyrazine (2,6-MP) and 2,3,5-tri-methyl-pyrazine (2,3,5-MP)) in porcine left anterior descending coronary artery (tertiary branch, O.D. </=1 mm). In 5-hydroxytryptamine (3 microM) precontracted preparations, cumulative administration (0.1-300 microM) of all pyrazine analogues caused an endothelium-independent, concentration-dependent relaxation. The relative inhibitory potency, as compared at concentration with which 50% relaxation occurred, was 2,3,5,6-MP>2,3,5-MP>EP>2,5-MP>/=2,6-MP>/=2,3-MP>2-MP. Besides, salbutamol and forskolin caused an endothelium-independent relaxation. The relaxation response of ligustrazine, salbutamol and forskolin was blunted in the presence of cis-N-(2-phenylcyclopentyl) azacyclotridec-1-en-2-amine (MDL 12330A) (10 microM, an adenylate cyclase inhibitor) and N-[2-((bromocinnamyl)amino)ethyl]-5-isoquinoline-sulphonamide (H-89, a protein kinase A inhibitor, 3 microM). Patch-clamp, whole-cell electrophysiological studies using single smooth muscle cells of the left anterior descending coronary artery revealed that ligustrazine (300 microM), salbutamol (30 microM) and forskolin (1 microM) inhibited the nifedipine-sensitive L-type Ca(2+) channels, and the inhibitory effect was eradicated by MDL 12330A (10 microM) and H-89 (1 microM). However, neither the Ca(2+)-dependent K(+) channel nor the ATP-dependent K(+) channel was modified by ligustrazine (300 microM). In conclusion, our results indicate that ligustrazine-mediated left anterior descending coronary artery relaxation is due to the activation of adenylate cyclase/protein kinase A cascade and the subsequent inhibition of nifedipine-sensitive, voltage-dependent L-type Ca(2+) channels. However, opening of K(+) channels seems to play no role in mediating the relaxation effect of ligustrazine.
authors.affiliation: Department of Pharmacology, Faculty of Medicine, Room 409B, Basic Medical Sciences Building, The Chinese University of Hong Kong, Shatin, New Territories, SAR, Hong Kong, PR China.
authors.forename: Alice Lai
authors.initials: AL
authors.lastname: Shan Au
authors.forename: Yiu Wa
authors.initials: YW
authors.lastname: Kwan
authors.forename: Ching Chi
authors.initials: CC
authors.lastname: Kwok
authors.forename: Rong-Zhen
authors.initials: RZ
authors.lastname: Zhang
authors.forename: Guo-Wei
authors.initials: GW
authors.lastname: He
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology; D020746:Calcium Channels, L-Type / Q000187:drug effects; D003331:Coronary Vessels / Q000187:drug effects*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000378:metabolism; D005260:Female; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects* / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011719:Pyrazines / Q000008:administration & dosage / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D013329:Structure-Activity Relationship; D013552:Swine
chemical_list: D020746:Calcium Channels, L-Type; D011719:Pyrazines; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium; C017953:tetramethylpyrazine