The effect of barium on [3H]noradrenalin release from the human neuroblastoma SH-SY5Y.
Replacement of Ca2+ with Ba2+ in HEPES-buffered saline stimulated [3H]noradrenalin release in the human neuroblastoma clone SH-SY5Y by up to 20% of the cell content in the absence of other secretory stimuli. The Ba(2+)-evoked release was inhibited by 85% by 3 microM tetrodotoxin and 95% by 5 microM nifedipine. Ba2+ also increased the potency of K(+)-evoked release of [3H]noradrenalin, as maximal release was observed with 60 mM K+ compared with the 100 mM K+ necessary to achieve maximal release in the presence of Ca2+. In contrast, replacing Ca2+ with Ba2+ had little effect on carbachol- and bradykinin-evoked release of [3H]noradrenalin. No evidence was obtained from studies on changes in [Ca2+]i (in response to 100 microM carbachol) using fura-2 that Ba2+ could enter intracellular stores in SH-SY5Y cells. Whole-cell patch-clamp studies showed that Ba2+ depolarizes SH-SY5Y cells as well as enhancing inward Ca2+ channel currents and shifting their voltage dependence to more negative values. These results are discussed in terms of the hypothesis that Ba2+ blocks K+ channels, leading to depolarization followed by opening of voltage-sensitive Na+ channels. This in turn opens voltage-sensitive L-type Ca2+ channels, which are coupled to the release of [3H]noradrenalin in SH-SY5Y cells.
Vaughan
P F
PF
Department of Cardiovascular Studies, University of Leeds, UK.
Kaye
D F
DF
Ball
S G
SG
Reeve
H L
HL
Peers
C
C
D001464:Barium / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects; D005089:Exocytosis; D006801:Humans; D009447:Neuroblastoma; D009474:Neurons / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D001464:Barium; D013779:Tetrodotoxin; D002217:Carbachol; D009543:Nifedipine; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine