Effects of substance P on nicotine-induced intracellular Ca2+ dynamics in bovine adrenal chromaffin cells.
Substance P (SP) is colocalized with ACh in splanchnic nerves that innervate into adrenal medulla and the peptide has been shown to inhibit nicotinic agonists-induced catecholamine secretion. To elucidate the effects of SP on cytosolic Ca2+ dynamics, the present study was conducted using fura-2-loaded isolated bovine adrenal chromaffin cells. Stimulation of the cells with nicotine (10-100 microM) produced a rapid rise of cytosolic Ca2+ concentration ([Ca2+]i), the peak level of which increased in a dose-dependent manner, followed by a gradual decay. In the presence of 10 microM SP, the dose-response relationship of the peak levels shifted downward. Quantitative analyses implied that SP inhibits the nicotine-induced Ca2+ influx in a noncompetitive manner. Nicotinic acetylcholine receptor is composed of two major functional domains: an agonist-binding site and an ionophore or channel domain. Agonist binding activates ionophore/channel domain and causes mainly Na+ influx. This Na+ influx depolarizes the cell and activates voltage-dependent Ca2+ channels. Based on this fact, the present results indicate that SP dose not block nicotine binding sites but interferes with other sites of nicotinic receptor/channel molecule, most probably a channel domain. It was suggested that SP colocalized with ACh in splanchnic nerves functions as a physiological modulator of catecholamine secretion by non-competitively suppressing ACh-induced cytosolic Ca2+ dynamics in bovine adrenal chromaffin cells.
Suzuki
S
S
Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Japan.
Habara
Y
Y
Kanno
T
T
D000313:Adrenal Medulla / Q000166:cytology / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D009538:Nicotine / Q000494:pharmacology*; D011978:Receptors, Nicotinic / Q000502:physiology; D013373:Substance P / Q000494:pharmacology*
D011978:Receptors, Nicotinic; D013373:Substance P; D009538:Nicotine; D002118:Calcium