Sympathetic regulation of vascular tone via noradrenaline and serotonin in the rat carotid body as revealed by intracellular calcium imaging

• We examined the sympathetic regulation of vascular tone in carotid body (CB).
• Cervical sympathetic nerve activity was increased in rats during inhalation of hypoxic gas.
• Noradrenaline increased intracellular Ca2+ levels in arteriolar smooth muscle cells.
• Serotonin increased intracellular Ca2+ levels in capillary pericytes.
• Chemosensory activity in CB may be indirectly enhanced by sympathetic nerves via regulating vascular tone.

Hypoxia-induced chemosensory activity in the carotid body (CB) may be enhanced by the sympathetic regulation of vascular tone in the CB. In the present study, we recorded cervical sympathetic nerve activity in rats exposed to hypoxia, and examined noradrenaline (NA)- and serotonin (5-HT)-induced intracellular Ca2+ ([Ca2+]i) responses in smooth muscle cells and pericytes in isolated blood vessels from the CB. Multifiber electrical activity recorded from the cervical sympathetic trunk was increased during the inhalation of hypoxic gas. NA induced [Ca2+]i increases in smooth muscle cells in arteriole specimens, whereas 5-HT did not cause any [Ca2+]i responses. However, NA did not induce [Ca2+]i increases in pericytes in capillaries, whereas 5-HT did and this response was inhibited by the 5-HT2 receptor antagonist, ketanserin. In conclusion, cervical sympathetic nerves enhanced by hypoxia may reduce blood flow in the CB in order to increase chemosensitivity. Thus, hypoxic chemosensitivity in the CB may involve a positive feedback mechanism via sympathetic nerves.