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

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.

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.

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.

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.