Abstract
In the present study, the effects on intracellular calcium concentration ([Ca2+]i) oscillations of the blockade of ether-a-go-go-related gene (ERG) K+channels and of Ca2+ influx through store-operated channels (SOC) activated by [Ca2+]i store depletion have been studied in GH3 cells by means of a combination of single-cell fura-2 microfluorimetry and whole-cell mode of the patch-clamp technique. Nanomolar concentrations (1–30 nM) of the piperidinic second-generation antihistamines terfenadine and astemizole and of the class III antiarrhythmic methanesulfonanilide dofetilide, by blocking ERG K+ channels, increased the frequency and the amplitude of [Ca2+]i oscillations in resting oscillating GH3 cells. These compounds also induced the appearance of an oscillatory pattern of [Ca2+]i in a subpopulation of nonoscillating GH3 cells. The effects of ERG K+ channel blockade on [Ca2+]i oscillations appeared to be due to the activation of L-type Ca2+ channels, because they were prevented by 300 nM nimodipine. By contrast, the piperazinic second-generation antihistamine cetirizine (0.01–30 μM), which served as a negative control, failed to affect ERG K+channels and did not interfere with [Ca2+]ioscillations in GH3 cells. Interestingly, micromolar concentrations of terfenadine and astemizole (0.3–30 μM), but not of dofetilide (10–100 μM), produced an inhibition of the spontaneous oscillatory pattern of [Ca2+]i changes. This effect was possibly related to an inhibition of SOC, because these compounds inhibited the increase of [Ca2+]iachieved by extracellular calcium reintroduction after intracellular calcium store depletion with the sarcoplasmic or endoplasmic reticulum calcium ATPase pump inhibitor thapsigargin (10 μM) in an extracellular calcium-free medium. The same inhibitory effect on [Ca2+]i oscillations and SOC was observed with the first-generation antihistamine hydroxyzine (1–30 μM), the more hydrophobic metabolic precursor of cetirizine. Collectively, the results of the present study obtained with compounds that interfere in a different concentration range with ERG K+ channels or SOC suggest that 1) ERG K+ channels play a relevant role in controlling the oscillatory pattern of [Ca2+]i in resting GH3 cells and 2) the inhibition of SOC might induce an opposite effect, i.e., an inhibition of [Ca2+]i oscillations.
Footnotes
- Received February 18, 2000.
- Accepted August 9, 2000.
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Send reprint requests to: Dr. Lucio Annunziato, M.D., Unit of Pharmacology, Department of Neurosciences, University of Naples Federico II, Via S. Pansini 5, 80131 Naples, Italy. E-mail:lannunzi{at}unina.it
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The study was supported by the following grants: Telethon 1058, National Research Council 97.04512. CT04, 97.01230. PF49, and 98.03149. CT04 (M.T.); Istituto Superiore di Sanità, Roma, Italy (Progetto sulle proprietà chimico-fisiche dei medicamenti e loro sicurezza d' uso), National Research Council 96.02074, 97.04559, 98.01048. CT04, and 98.00062. PF31 (PS Biotecnologie 5%), Murst Cofinanziamento 1998, and Regione Campania (P.O.P. and Legge 41) (L.A.).
- The American Society for Pharmacology and Experimental Therapeutics
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