Role of [Na+]i and [Ca2+]i in nicotine-induced norepinephrine release from bovine adrenal chromaffin cells.
Intracellular free sodium ([Na+]i) and calcium ([Ca2+]i) concentrations were determined by sodium-binding benzofuran isophthalate (SBFI) and fura 2 microfluorimetry, respectively, in bovine adrenal chromaffin cells (BCC). Validation of SBFI microfluorimetry by in vitro and in vivo calibration revealed a reliable assessment of [Na+]i within a range of 1-30 mM in single BCC. Nicotine (0.1-10 microM) induced concentration-dependent increases of both [Na+]i (from 3.3 +/- 0.1 to 25.6 +/- 0.4 mM, n = 76, P < 0.001) and [Ca2+]i (from 64 +/- 1 to 467 +/- 16 nM, n = 87, P < 0.001), which were accompanied by an increase in [3H]norepinephrine (NE) release. Consistent with an exocytotic release mechanism, nicotine-induced increments of [Ca2+]i and [3H]NE release were reduced under calcium-free conditions and by gadolinium chloride (40 microM), whereas [Na+]i was not affected. In contrast, a parallel attenuation of nicotine-evoked changes in [Na+]i, [Ca2+]i, and [3H]NE release was observed during reduction of the extracellular sodium concentration. The nicotine-evoked responses were neutralized by the nicotinic receptor antagonist hexamethonium (100 microM) but not by blockade of voltage-dependent sodium channels (1 microM tetrodotoxin). In conclusion, the nicotine-induced exocytotic release of [3H]NE is triggered by an increase in [Ca2+]i, which is facilitated by sodium influx through the nicotinic receptor ionophore.
Gerber
S H
SH
Department of Cardiology, University of Heidelberg, Germany.
Haunstetter
A
A
Krüger
C
C
Kaufmann
A
A
Nobiling
R
R
Haass
M
M
D000311:Adrenal Glands / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D001572:Benzofurans; D002118:Calcium / Q000502:physiology*; D002138:Calibration; D002417:Cattle; D002838:Chromaffin System / Q000166:cytology / Q000378:metabolism*; D004988:Ethers, Cyclic; D005456:Fluorescent Dyes; D005470:Fluorometry; D016257:Fura-2; D007425:Intracellular Membranes / Q000378:metabolism*; D009538:Nicotine / Q000494:pharmacology*; D009638:Norepinephrine / Q000378:metabolism*; D009994:Osmolar Concentration; D012964:Sodium / Q000502:physiology*
D001572:Benzofurans; D004988:Ethers, Cyclic; D005456:Fluorescent Dyes; C061665:sodium-binding benzofuran isophthalate; D009538:Nicotine; D012964:Sodium; D002118:Calcium; D016257:Fura-2; D009638:Norepinephrine