L-type calcium channels in sympathetic α3β2-nAChR-mediated cerebral nitrergic neurogenic vasodilation

Aim 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 Cav1.2 and Cav1.3 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 Cav1.2 and Cav1.3 channels were expressed in porcine SCG and peri‐vascular nerve terminals. Conclusion 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.