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

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Acta Physiologica

Published online on

Abstract

Aim Nicotine stimulation of α3β2‐nicotinic acetylcholine receptors (α3β2‐nAChRs) located on sympathetic nerves innervating basilar arteries causes calcium‐dependent norepinephrine 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 perivascular 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, norepinephrine‐release, and inward‐currents were evaluated in rat superior cervical ganglion (SCG) neurons, perivascular 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 neurons and reduced nicotine‐induced norepinephrine release from perivascular 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 perivascular nerve terminals. Conclusion The sympathetic neuronal calcium‐influx through L‐type calcium‐channels is modulated by α3β2‐nAChRs. This calcium‐influx causes norepinephrine release, initiating sympathetic‐parasympathetic (axo‐axonal) interaction‐induced nitrergic dilation of porcine basilar arteries. This article is protected by copyright. All rights reserved.