Pharmacological blockade of ERG K(+) channels and Ca(2+) influx through store-operated channels exerts opposite effects on intracellular Ca(2+) oscillations in pituitary GH(3) cells.
In the present study, the effects on intracellular calcium concentration ([Ca(2+)](i)) oscillations of the blockade of ether-a-go-go-related gene (ERG) K(+) channels and of Ca(2+) influx through store-operated channels (SOC) activated by [Ca(2+)](i) store depletion have been studied in GH(3) 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 [Ca(2+)](i) oscillations in resting oscillating GH(3) cells. These compounds also induced the appearance of an oscillatory pattern of [Ca(2+)](i) in a subpopulation of nonoscillating GH(3) cells. The effects of ERG K(+) channel blockade on [Ca(2+)](i) oscillations appeared to be due to the activation of L-type Ca(2+) channels, because they were prevented by 300 nM nimodipine. By contrast, the piperazinic second-generation antihistamine cetirizine (0.01-30 microM), which served as a negative control, failed to affect ERG K(+) channels and did not interfere with [Ca(2+)](i) oscillations in GH(3) cells. Interestingly, micromolar concentrations of terfenadine and astemizole (0.3-30 microM), but not of dofetilide (10-100 microM), produced an inhibition of the spontaneous oscillatory pattern of [Ca(2+)](i) changes. This effect was possibly related to an inhibition of SOC, because these compounds inhibited the increase of [Ca(2+)](i) achieved by extracellular calcium reintroduction after intracellular calcium store depletion with the sarcoplasmic or endoplasmic reticulum calcium ATPase pump inhibitor thapsigargin (10 microM) in an extracellular calcium-free medium. The same inhibitory effect on [Ca(2+)](i) oscillations and SOC was observed with the first-generation antihistamine hydroxyzine (1-30 microM), 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 [Ca(2+)](i) in resting GH(3) cells and 2) the inhibition of SOC might induce an opposite effect, i.e., an inhibition of [Ca(2+)](i) oscillations.
Secondo
A
A
Unit of Pharmacology, Department of Neuroscience, School of Medicine, University of Naples Federico II, Naples, Italy.
Taglialatela
M
M
Cataldi
M
M
Giorgio
G
G
Valore
M
M
Di Renzo
G
G
Annunziato
L
L
D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D016589:Astemizole / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000378:metabolism; D027682:Cation Transport Proteins; D002478:Cells, Cultured; D017332:Cetirizine / Q000494:pharmacology; D004594:Electrophysiology; D051638:Ether-A-Go-Go Potassium Channels; D006634:Histamine H1 Antagonists / Q000494:pharmacology*; D006919:Hydroxyzine / Q000494:pharmacology; D051036:Large-Conductance Calcium-Activated Potassium Channels; D009553:Nimodipine / Q000494:pharmacology; D010627:Phenethylamines / Q000494:pharmacology; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism; D024681:Potassium Channels, Calcium-Activated; D024642:Potassium Channels, Voltage-Gated; D051381:Rats; D051640:Small-Conductance Calcium-Activated Potassium Channels; D013449:Sulfonamides / Q000494:pharmacology; D016593:Terfenadine / Q000494:pharmacology
D000889:Anti-Arrhythmia Agents; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D027682:Cation Transport Proteins; D051638:Ether-A-Go-Go Potassium Channels; D006634:Histamine H1 Antagonists; C092509:KCNH6 protein, human; C109500:Kcnh6 protein, rat; D051036:Large-Conductance Calcium-Activated Potassium Channels; D010627:Phenethylamines; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D024642:Potassium Channels, Voltage-Gated; D051640:Small-Conductance Calcium-Activated Potassium Channels; D013449:Sulfonamides; D006919:Hydroxyzine; D009553:Nimodipine; D016593:Terfenadine; D016589:Astemizole; C063533:dofetilide; D002118:Calcium; D017332:Cetirizine