The Effect of Barium on [³H]Noradrenalin Release from the Human Neuroblastoma SH‐SY5Y

Abstract

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.

Detection of changes in membrane potential by magnetic resonance imaging

“…For this reason, in this experiment, Ba 2+ was utilized to decrease the K + permeability of the cell membrane, resulting in depolarization of the resting potential. Ba 2+ -induced depolarization in SH-SY5Y and Jurkat cells has been reported in previous studies 27,28 .…”

“…Ba 2+ was chosen because it inhibits several types of two-pore-domain potassium channels 37,38 , which predominantly regulate the resting membrane potential. Previous studies have confirmed that Ba 2+ depolarizes the membrane potential in SH-SY5Y and Jurkat cells 39,40 .…”

Muscarinic (Mi) receptor‐mediated inhibition of K+‐evoked [3H]‐noradrenaline release from human neuroblastoma (SH‐SY5Y) cells via inhibition of L‐ and N‐type Ca2+ channels

“…To examine this possibility, we investigated the ability of muscarine to inhibit PH]-NA release evoked by other stimuli. We have previously shown that Ba2+ evokes release in these cells via depolarization and Ca2" influx through voltage-gated Ca2" channels (Vaughan et al, 1993b). Figure 3 shows that release evoked by substitution of extracellular Ca2" with Ba2+ (2.5 mM) for 4 min, and also by 4 min exposure to 28 JIM veratridine (another commonly used depolarizing secretagogue) can be inhibited to similar degrees as K+-evoked release with 300 jAM muscarine.…”