Article date: October 1994
By: R.L. McDonald, P.F.T. Vaughan, C. Peers, in Volume 113, Issue 2, pages 621-627
Human neuroblastoma (SH‐SY5Y) cells were preincubated with [3H]‐noradrenaline ([3H]‐NA) in the presence of 0.2 mm pargyline to examine the modulation of K+‐evoked [3H]‐NA release by muscarinic agonists.
Release of [3H]‐NA evoked by 4 min exposure to 100 mm K+ could be partially inhibited by 5 μm nifedipine and partially inhibited by 100 nm ω‐conotoxin GVIA (ω‐CgTx). When nifedipine and (ω‐CgTx were added together, evoked release was inhibited by approximately 93%.
K+‐evoked [3H]‐NA release was inhibited by > 90% by pretreatment of cells for 2 min with muscarine, carbachol or oxotremorine methiodide (each at 300 μm). For muscarine, inhibition of evoked release was both time‐ and concentration‐dependent and was reversible. Muscarine also inhibited [3H]‐NA release evoked by veratridine (28 μm) and replacement of extracellular Ca2+ with Ba2+, but not that evoked by the Ca2+ ionophore, A23187 (19 μm).
Residual K+‐evoked [3H]‐NA release measured in the presence of either nifedipine (5 μm) or ω‐CgTx (100 nm) was inhibited by muscarine with a similar potency as release evoked in the absence of either Ca2+ channel blocker. Pretreatment of cells for 16–24 h with pertussis toxin (200 ng ml−1) did not affect K+‐evoked release per se or the ability of muscarine to inhibit such release.
Muscarinic inhibition of K+‐evoked [3H]‐NA release was potently antagonized by pirenzepine (pA2 8.14) and by hexahydrosiladiphenidol (pA2 9.03), suggesting the involvement of an M1 receptor.
Our results demonstrate that 100 mm K+‐evoked release of [3H]‐NA from the human neuroblastoma is mediated by activation of both L‐ and N‐type Ca2+ channels. Activation of muscarinic M1 receptors can inhibit release via a pertussis toxin‐insensitive mechanism which involves non‐selective inhibition of L‐ and N‐type Ca2+ channels.
Human neuroblastoma (SH‐SY5Y) cells were preincubated with [3H]‐noradrenaline ([3H]‐NA) in the presence of 0.2 mm pargyline to examine the modulation of K+‐evoked [3H]‐NA release by muscarinic agonists.
Release of [3H]‐NA evoked by 4 min exposure to 100 mm K+ could be partially inhibited by 5 μm nifedipine and partially inhibited by 100 nm ω‐conotoxin GVIA (ω‐CgTx). When nifedipine and (ω‐CgTx were added together, evoked release was inhibited by approximately 93%.
K+‐evoked [3H]‐NA release was inhibited by > 90% by pretreatment of cells for 2 min with muscarine, carbachol or oxotremorine methiodide (each at 300 μm). For muscarine, inhibition of evoked release was both time‐ and concentration‐dependent and was reversible. Muscarine also inhibited [3H]‐NA release evoked by veratridine (28 μm) and replacement of extracellular Ca2+ with Ba2+, but not that evoked by the Ca2+ ionophore, A23187 (19 μm).
Residual K+‐evoked [3H]‐NA release measured in the presence of either nifedipine (5 μm) or ω‐CgTx (100 nm) was inhibited by muscarine with a similar potency as release evoked in the absence of either Ca2+ channel blocker. Pretreatment of cells for 16–24 h with pertussis toxin (200 ng ml−1) did not affect K+‐evoked release per se or the ability of muscarine to inhibit such release.
Muscarinic inhibition of K+‐evoked [3H]‐NA release was potently antagonized by pirenzepine (pA2 8.14) and by hexahydrosiladiphenidol (pA2 9.03), suggesting the involvement of an M1 receptor.
Our results demonstrate that 100 mm K+‐evoked release of [3H]‐NA from the human neuroblastoma is mediated by activation of both L‐ and N‐type Ca2+ channels. Activation of muscarinic M1 receptors can inhibit release via a pertussis toxin‐insensitive mechanism which involves non‐selective inhibition of L‐ and N‐type Ca2+ channels.
DOI: 10.1111/j.1476-5381.1994.tb17035.x
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