Capacitative Ca2+ entry into Xenopus oocytes is sensitive to omega-conotoxins GVIA, MVIIA and MVIIC.
We have studied capacitative Ca2+ entry into Xenopus oocytes by depleting intracellular Ca2+ stores with inositol 1,4,5-trisphosphate or thapsigargin. Capacitative Ca2+ entry was evoked by hyperpolarisation and monitored via the Ca(2+)-activated Cl- current. Hyperpolarisation-evoked currents increased with extracellular [Ca2+] in the range 0.9-5 mM, and were reversibly inhibited by extracellular Mg2+ (0.1-10 mM) by up to 60%. Currents were decreased by the voltage-gated Ca2+ channel antagonists omega-conotoxin GVIA, MVIIA and MVIIC (0.3-10 microM) and the inhibition of Ca2+ entry in individual oocytes by omega-conotoxins GVIA and MVIIA was highly heterogeneous, but not additive. Flunarizine (10 microM) and the imidazoles SK&F 96365 (10 microM), miconazole (40 microM) and econazole (40 microM) partly blocked Ca2+ entry. Ca2+ entry was unaffected by calciseptine (300 nM) or alpha-bungarotoxin (1 microM). The possibility that these compounds might inhibit the Ca(2+)-activated Cl- current rather than capacitative Ca2+ entry itself was examined by recording the Cl- current activated by the increase in [Ca2+]i activated by the flash photolysis of caged Ca2+. Eicosatetraynoic acid (2-10 microM) markedly inhibited, and La3+ (1 mM but not 100 microM) potentiated the increase in Ca(2+)-activated Cl- current. In contrast, omega-conotoxins and Mg2+ had no effect on the Ca(2+)-activated Cl- current itself. These findings support the hypothesis that capacitative Ca2+ entry into Xenopus oocytes occurs through channels with a pharmacology similar to that of neuronal non-L type voltage-gated Ca2+ channels.
Departamento de Farmacología, Facultad de Medicina, Universidad Autónoma de Madrid, Spain. rlomax@fs1.ho.man.ac.uk
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Lomax
C J
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Herrero
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García-Palomero
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García
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Montiel
D015117:5,8,11,14-Eicosatetraynoic Acid / Q000494:pharmacology; D000085:Acetates / Q000528:radiation effects; D000818:Animals; D002038:Bungarotoxins / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000145:classification / Q000187:drug effects* / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D004464:Econazole / Q000494:pharmacology; D004546:Elapid Venoms / Q000494:pharmacology; D005029:Ethylenediamines / Q000528:radiation effects; D005444:Flunarizine / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D017136:Ion Transport / Q000187:drug effects; D007811:Lanthanum / Q000494:pharmacology; D008825:Miconazole / Q000494:pharmacology; D009544:Niflumic Acid / Q000494:pharmacology; D009865:Oocytes / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology*; D010716:Phosphatidylinositols / Q000502:physiology; D010782:Photolysis; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014982:Xenopus laevis; D020866:omega-Conotoxin GVIA; D020960:omega-Conotoxins
D000085:Acetates; D002038:Bungarotoxins; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002712:Chlorides; D004546:Elapid Venoms; D005029:Ethylenediamines; D007093:Imidazoles; D010455:Peptides; D010716:Phosphatidylinositols; D020960:omega-Conotoxins; C053157:omega-conotoxin receptor; D015117:5,8,11,14-Eicosatetraynoic Acid; C075851:omega-conotoxin-MVIIC; C057014:DM-nitrophen; C067971:calciseptine; D009544:Niflumic Acid; D007811:Lanthanum; D004464:Econazole; C078452:ziconotide; D008825:Miconazole; D015544:Inositol 1,4,5-Trisphosphate; D020866:omega-Conotoxin GVIA; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D005444:Flunarizine; D002118:Calcium