L-type calcium channels in sympathetic α3β2-nAChR-mediated cerebral nitrergic neurogenic vasodilation.
OBJECTIVE
Nicotine stimulation of α3β2-nicotinic acetylcholine receptors (α3β2-nAChRs) located on sympathetic nerves innervating basilar arteries causes calcium-dependent noradrenaline release, leading to activation of parasympathetic nitrergic nerves and dilation of basilar arteries. This study aimed to investigate the major subtype of calcium channels located on cerebral peri-vascular sympathetic nerves, which is involved in nicotine-induced α3β2-nAChR-mediated nitrergic vasodilation in basilar arteries.


METHODS
Nicotine- and transmural nerve stimulation (TNS)-induced dilation of isolated porcine basilar arteries was examined using in vitro tissue bath. Nicotine-induced calcium influx, nicotine-induced noradrenaline release and nicotine-induced inward currents were evaluated in rat superior cervical ganglion (SCG) neurones, peri-vascular sympathetic nerves of porcine basilar arteries and α3β2-nAChRs-expressing oocytes respectively. mRNA and protein expression of Cav 1.2 and Cav 1.3 channels were detected by RT-PCR, Western blotting and immunohistochemistry.


RESULTS
Nicotine-induced vasodilation was not affected by ω-agatoxin TK (selective P/Q-type calcium channel blocker) or ω-conotoxin GVIA (N-type calcium channel blocker). The vasodilation, however, was inhibited by nicardipine (L-type calcium channel blocker) in concentrations which did not affect TNS-induced vasodilation, suggesting the specific blockade. Nicardipine concentration-dependently inhibited nicotine-induced calcium influx in rat SCG neurones and reduced nicotine-induced noradrenaline release from peri-vascular sympathetic nerves of porcine basilar arteries. Nicardipine (10 μm), which significantly blocked nicotine-induced vasorelaxation by 70%, did not appreciably affect nicotine-induced inward currents in α3β2-nAChRs-expressing oocytes. Furthermore, the mRNAs and proteins of Cav 1.2 and Cav 1.3 channels were expressed in porcine SCG and peri-vascular nerve terminals.


CONCLUSIONS
The sympathetic neuronal calcium influx through L-type calcium channels is modulated by α3β2-nAChRs. This calcium influx causes noradrenaline release, initiating sympathetic-parasympathetic (axo-axonal) interaction-induced nitrergic dilation of porcine basilar arteries.
Institute of Pharmacology & Toxicology, Tzu Chi University, Hualien, Taiwan; Center for Vascular Medicine, College of Life Sciences, Tzu Chi University, Hualien, Taiwan.
C Y-C
CY
Wu
R H-C
RH
Lee
P-Y
PY
Chen
A P-Y
AP
Tsai
M-F
MF
Chen
J-S
JS
Kuo
T J-F
TJ
Lee
D000818:Animals; D001488:Basilar Artery / Q000294:innervation / Q000378:metabolism*; D015153:Blotting, Western; D001921:Brain / Q000098:blood supply; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D002560:Cerebrovascular Circulation / Q000502:physiology; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D007150:Immunohistochemistry; D008297:Male; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D026602:Nitrergic Neurons / Q000378:metabolism; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D011978:Receptors, Nicotinic / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013552:Swine; D013564:Sympathetic Nervous System / Q000502:physiology*; D014664:Vasodilation / Q000502:physiology*
D020746:Calcium Channels, L-Type; D018722:Nicotinic Agonists; D011978:Receptors, Nicotinic; C419362:nicotinic receptor alpha3beta2; D009538:Nicotine
Cav1.2 and Cav1.3 channels; L-type voltage-dependent Ca2+ channels; cerebral peri-vascular sympathetic nerves; neurogenic vasodilation; noradrenaline release; α3β2-nicotinic acetylcholine receptor