Ionomycin induced changes in intracellular free calcium in SH-SY5Y human neuroblastoma cells: sources of calcium and effects on [3H]-noradrenaline release.
In adherent SH-SY5Y human neuroblastoma cells cultured for 14 days to promote uptake and release of [3H]-noradrenaline, ionomycin induced a biphasic elevation of the intracellular [Ca2+] ([Ca2+]i). This consisted of a rapid transient elevation followed by a marked, persistent secondary elevation. Further study indicated that the peak [Ca2+]i elevation was dependent upon intracellular Ca2+ whilst the secondary elevation was dependent upon extracellular Ca2+. This profile of response and dependence upon intracellular and extracellular sources of Ca2+ was similar to that evoked by the muscarinic agonist, methacholine but was independent of inositol 1,4,5-trisphosphate generation. Ionomycin also stimulated the release of [3H]-noradrenaline from preloaded cells. Both intracellular and extracellular sources of Ca2+ were needed for the full response and synergised to effect release. Thus, in adherent SH-SY5Y cells, ionomycin elevates [Ca2+]i in a complex way in a manner partly analogous to the elevation of [Ca2+]i by agonists of phosphoinositidase C-linked receptors. Furthermore the effects of [Ca2+]i elevation on [3H]-noradrenaline release by these two processes are similar. Such functional consequences may, however, differ under circumstances where the profile and source of Ca2+ for ionomycin-mediated changes differs to that of receptor agonists.
Purkiss
J R
JR
Department of Cell Physiology and Pharmacology, University of Leicester, UK.
Willars
G B
GB
D002118:Calcium / Q000032:analysis; D005110:Extracellular Space / Q000737:chemistry; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D015759:Ionomycin / Q000494:pharmacology*; D007476:Ionophores / Q000494:pharmacology; D009447:Neuroblastoma / Q000473:pathology*; D009638:Norepinephrine / Q000378:metabolism; D014316:Tritium; D014407:Tumor Cells, Cultured / Q000737:chemistry
D007476:Ionophores; D014316:Tritium; D015759:Ionomycin; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium; D009638:Norepinephrine