Mechanisms responsible for the in vitro relaxation of ligustrazine on porcine left anterior descending coronary artery.
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.
Shan Au
Alice Lai
AL
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.
Kwan
Yiu Wa
YW
Kwok
Ching Chi
CC
Zhang
Rong-Zhen
RZ
He
Guo-Wei
GW
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
D020746:Calcium Channels, L-Type; D011719:Pyrazines; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium; C017953:tetramethylpyrazine