L-type calcium channels in sympathetic alpha 3 beta 2-nAChR-mediated cerebral nitrergic neurogenic vasodilation

Aim Nicotine stimulation of alpha 3 beta 2-nicotinic acetylcholine receptors ( alpha 3 beta 2-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 alpha 3 beta 2-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 alpha 3 beta 2-nAChRs-expressing oocytes respectively. mRNA and protein expression of Ca sub(v)1.2 and Ca sub(v)1.3 channels were detected by RT-PCR, Western blotting and immunohistochemistry. Results Nicotine-induced vasodilation was not affected by omega -agatoxin TK (selective P/Q-type calcium channel blocker) or omega -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 mu m), which significantly blocked nicotine-induced vasorelaxation by 70%, did not appreciably affect nicotine-induced inward currents in alpha 3 beta 2-nAChRs-expressing oocytes. Furthermore, the mRNAs and proteins of Ca sub(v)1.2 and Ca sub(v)1.3 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 alpha 3 beta 2-nAChRs. This calcium influx causes noradrenaline release, initiating sympathetic-parasympathetic (axo-axonal) interaction-induced nitrergic dilation of porcine basilar arteries.